user129557: If I want to know the price of bitcoin, I can go to coinmarketcap, but where do they take it from? Where does the coinmarketcap provider get it from, and what is the ultimate source of this value?
Everyone seems to agree upon roughly the same BTC to USD rate. an ignorant like me can naively think it's taken from a centralized database
Clarification: This is a technical question, coinmarketcap.com is ultimately a web page and regardless of the rules that govern the price, I'm trying to understand if there are some technical people able to edit a number in some databases affecting everyone's perception. "tamper with the price by selling/buying" is a way of playing by the rules imho, not the kind of answer I'm looking for.
Follow up question: What if an exchange reports false information?

user129367: The price is the equilibrium between all buying and selling orders. People offer to buy or sell their Bitcoin with a positive or negative premium. When you consolidate all these prices (e.g. market information) you get the price that is currently displayed at coinmarketcap or an exchange of your choice.

user21282: This has been mentioned in other comments, but I thought it would be good to highlight it further: the answer to this question is exactly the same that for any other commodity.
Commodity means an asset that is highly fungible, i.e., you can replace two items of that type for one another entirely or almost entirely. Examples of fungible assets besides bitcoins include dollars, stocks of a given company, gold bars, crude oil or rice. Examples of non-fungible assets include houses, works of art and, unsurprisingly NFTs.
And as other answers mentioned, commodities are traded in exchanges, which are basically systems for matching buy bids (each of which sets a maximum buy price) to sell offers (each of which sets a minimum sell price). Exchanges tend to be few and large since the more buyers and sellers in a given system, the faster you are likely to get your sale through.
In any such exchange system, all we can know is what buy/sell offers people have made, and then try to come up with a decent "value" from this continuous stream of bids using some algorithm. A broker might then use such algorithm to set their price for a given commodity so that less specialized/smaller buyers can buy more conveniently, but ultimately the broker will be selling commodities they bought with that ever evolving offer system.
Of course, if someone buys too high, or sells too low, they will lose money so the price tends to be metastable around a given value in the short term, until other external factors alter the value perception. But there can also be a tradeoff, as buying high and selling low also mean you will get the trade faster in case you need the money urgently for something else, or if you've learned before others of some information that implies that the asset value will fall dramatically in the near future. A good example of that can be seen in the movie Margin Call about the 2007 financial crisis.
I think the only guarantee that traditional exchanges are not rigged by hiding/delaying information for someone's benefit is trust in their reputation and legal repercussions of doing so should they be caught. One thing that people who don't feel that this is enough could do is try to do create more decentralized systems, e.g. Ethereum based. The most notable one appears to be Uniswap (thanks to Boris in the comments). Wikipedia mentions that:

Uniswap’s average daily trading volume was US$220 million in October 2020

and their daily volumes are reported at: https://info.uniswap.org/#/

user208: There is no "the" BTC price.
There are exchanges, where people offer to sell and buy BTC for USD and other currencies, at certain prices. Those exchanges generally report the last price at which some trade happened. Generally, prices will move in tandem across multiple exchanges, but there are always small deviations.
There are indexers which aggregate trade data from multiple exchanges, and compute weighted averages over them.

129557: <p>If I want to know the price of bitcoin, I can go to coinmarketcap, but where do they take it from? Where does the coinmarketcap provider get it from, and what is the ultimate source of this value?</p>
<p>Everyone seems to agree upon roughly the same BTC to USD rate. an ignorant like me can naively think it's taken from a centralized database</p>
<p>Clarification: This is a technical question, coinmarketcap.com is ultimately a web page and regardless of the rules that govern the price, I'm trying to understand if there are some technical people able to edit a number in some databases affecting everyone's perception. &quot;tamper with the price by selling/buying&quot; is a way of playing by the rules imho, not the kind of answer I'm looking for.</p>
<p>Follow up question: What if an exchange reports false information?</p>
 129367: <p>The price is the equilibrium between all buying and selling orders. People offer to buy or sell their Bitcoin with a positive or negative premium. When you consolidate all these prices (e.g. market information) you get the price that is currently displayed at coinmarketcap or an exchange of your choice.</p>
 21282: <p>This has been mentioned in other comments, but I thought it would be good to highlight it further: the answer to this question is exactly the same that for any other <a href="https://en.wikipedia.org/wiki/Commodity" rel="nofollow noreferrer">commodity</a>.</p>
<p>Commodity means an asset that is highly <a href="https://en.wikipedia.org/wiki/Fungibility" rel="nofollow noreferrer">fungible</a>, i.e., you can replace two items of that type for one another entirely or almost entirely. Examples of fungible assets besides bitcoins include dollars, stocks of a given company, gold bars, crude oil or rice. Examples of non-fungible assets include houses, works of art and, unsurprisingly NFTs.</p>
<p>And as other answers mentioned, commodities are traded in exchanges, which are basically systems for matching buy bids (each of which sets a maximum buy price) to sell offers (each of which sets a minimum sell price). Exchanges tend to be few and large since the more buyers and sellers in a given system, the faster you are likely to get your sale through.</p>
<p>In any such exchange system, all we can know is what buy/sell offers people have made, and then try to come up with a decent &quot;value&quot; from this continuous stream of bids using some algorithm. A broker might then use such algorithm to set their price for a given commodity so that less specialized/smaller buyers can buy more conveniently, but ultimately the broker will be selling commodities they bought with that ever evolving offer system.</p>
<p>Of course, if someone buys too high, or sells too low, they will lose money so the price tends to be metastable around a given value in the short term, until other external factors alter the value perception. But there can also be a tradeoff, as buying high and selling low also mean you will get the trade faster in case you need the money urgently for something else, or if you've learned before others of some information that implies that the asset value will fall dramatically in the near future. A good example of that can be seen in the movie <a href="https://en.wikipedia.org/wiki/Margin_Call" rel="nofollow noreferrer">Margin Call</a> about the 2007 financial crisis.</p>
<p>I think the only guarantee that traditional exchanges are not rigged by hiding/delaying information for someone's benefit is trust in their reputation and legal repercussions of doing so should they be caught. One thing that people who don't feel that this is enough could do is try to do create more decentralized systems, e.g. Ethereum based. The most notable one appears to be <a href="https://en.wikipedia.org/wiki/Uniswap" rel="nofollow noreferrer">Uniswap</a> (thanks to Boris in the comments). Wikipedia mentions that:</p>
<blockquote>
<p>Uniswap’s average daily trading volume was US$220 million in October 2020</p>
</blockquote>
<p>and their daily volumes are reported at: <a href="https://info.uniswap.org/#/" rel="nofollow noreferrer">https://info.uniswap.org/#/</a></p>
 208: <p>There is <em>no</em> &quot;the&quot; BTC price.</p>
<p>There are exchanges, where people offer to sell and buy BTC for USD and other currencies, at certain prices. Those exchanges generally report the last price at which some trade happened. Generally, prices will move in tandem across multiple exchanges, but there are always small deviations.</p>
<p>There are indexers which aggregate trade data from multiple exchanges, and compute weighted averages over them.</p>
