The best way to find an agent is probably through referrals, (90 % of my business, and most agents, is referral based). If you don't have a network to tap into, then you can always "interview" them either through their websties & e-mail, or at Open Houses, and lots of other ways. Here's what I would consider good interview questions:
1) How many buyers did you place in the last 3 years?
2) How long have you been practicing?
3) What is your focus area?
4) Why should I pick you?
You're looking for someone who has done at least 20 transactions before, and more is usually better. You probably want someone who's personality and style fits with your own. If your analytical, find someone who also is, etc, etc.
As for commissions, I'd like to point out that in the state of MA, from a LEGAL perspective, the various courts have determined that 'both the seller and the buyer share in paying the commission. That is because if the buyer doesn't bring the money, there is no commission, so they both contribute to a commission event equally. However, on the HUD statements (they are like invoices for housing transactions), it shows up 100% on the sellers side, so it is conventional to say that the seller pays all commissions. I know that's probably a little overly complicated, but there are cases where the distinction is important, even if it isn't widely understood. Personally, I'd like to see the HUDs altered to reflect the legal perspective, as I think it would raise the profile of buyer agency and protect consumers better, but I don't think that will happen in my lifetime.