Is it suspicious for a conference abstract submission to be subordinated to registration? My PhD advisor and I wish to participate to a specific international conference in our field. 

The program seems legitimate and part of the scientific committee are respected researchers of my field, with whom we have already worked in the past. Therefore I am not questioning the academic relevancy of the conference.

On the other hand, the organization is operated by a company, and I am not at ease with their methods. Mainly, the registration fee (500€) must be paid before submitting any abstract and it is not possible to know whether the abstract has been accepted before committing.

Beside the frustration (a conference is a big investment in our budget), I find this unusual, if not fishy. This is the first time my advisor is confronted with the situation, and they are conflicted about this too.

As a side point, their privacy policy includes an agreement to transmit my academic information to "marketing partners", which I am not at ease either.

Should I be worried?

EDIT after investigating a bit more. The organizer is not exactly a company, but a "non-profit private organisation". 

UPDATE after contacting the organizers. The website actually gives the option to pay later, as long as the registration is placed. Ultimately, the admission decision will be issued before the payment deadline, although that was not apparent unless you create an account and place the order first.
€500 is within the normal range for an international conference, but the mandatory subscription before getting the notification of acceptance is indeed a bit suspicious. 

However there are some conferences which work in the following way: pretty much any abstract submitted is accepted (except if out of scope, I guess) and is supposed to be presented at the conference. The selection process happens when a subset of the abstracts are accepted for publication as a full paper in a journal issue. I'm not very familiar with this setting myself, but I assume that it might make sense for such a conference to make sure that the authors attend and present their work even if it's not selected for the journal issue.