Receiving gift from student before grading MSc thesis. Is it ethical? As a follow up on this question I am wondering whether it is ethical to receive gifts from students before grading their MSc thesis (or any other project where students feel like they need to thank you for).

Lately I have encountered this situation where a student gave me a present before I was able to fully grade his work. The student had to go abroad and wouldn't be able to drop by after grading. The gift was rather small, just a few bottles of good quality beers which are not that expensive where I'm from. He also said: "you can drink this when grading my work, ha ha". We got along quite well, so at that time I didn't feel like it was some sort of bribe (which I still don't feel like it was).

Generally, I don't have any problem in accepting gifts as they tend to be rather small. However, a month after receiving this gift and finishing my grading for his work I was starting to think whether I have made the right decision by accepting his gift.
In my opinion you are asking yourself the wrong question. The important problem is not if it feels like a bribe to you, but if it could look like a bribe to others. 

Let's say you have another student whose thesis you are grading at the same time and he ends up with a worse grade. This might have been an objective decision, but still, if this other student now hears about the gift you got, he will start to wonder if maybe giving you a nice gift would have gotten him the same grade.

Since the gift is quite small, you are most likely legally in the clear, however in my opinion, ethically it wasn't the right thing to do. It is probably to late to return the gift right now, but for similar future situations, it is probably better to decline gifts until the grade is set in stone. Not only from an ethical point of view but also since it will give you an aura of fairness and incorruptibility at the low cost of a few cheap beers.