Realtors in general get paid commission based on the sales price. Both the buyers and sellers agent get paid more commission the higher it goes for.
However, a realtor has a code of ethics if he is representing the buyers and a good one will get you the best price even if it means money out of their pocket.
Speaking of pockets. One issue is pocket listings. Last two places I bought were both pocket listings. What that means is realtor who got it pretty much mainly showed it themselves and buyers agents had trouble showing property. Although according to MLS that is not allowed.
First house seller had a deal with agent she would get a flat fee of 10K if she sold it herself. If it came in though MLS in a buyers broker deal the commission was 5% which at the time was around 15k. So buyers broker had to pay 5k more for owners to break even. Second time seller had a deal with 3.5% commission if sellers agent sold it vs. 5% on MLS>
Normally brokers want mls as they get the bigger audience, in both my cases buyers wanted to sell quick and priced it right. However, I took risk that agent is working for seller not me so I had to do my homework to make sure I did not over pay which was stressful.