This should review how many years they have been in the business and look for company awards. The experienced agents should have a history of production and service awards. You can also google the agents name and review what websites they link with.
Interview the agent and ask them questions and have them show you what they have accomplished in the buisiness.
Your profile says that you are a Home Buyer.
If I were a home buyer I would interview a couple of Realtors (there is a difference between a REALTOR and a real estate agent. Realtors have to agree to abide by a code of ethics.).
Interview Realtors from different companies (meaning not three associates from the same firm). I (being unashamedly biased) suggest the local Keller Williams office as a place to start.
The reason I say interview them is that buying or selling a home is a complex transaction. You will be dealing with the professional you select for quite a while, so you need someone with whom you can relate.
I think the number of transactions is important, but for more important is someone that will listen to your needs, not sell you on something.
Someone that demonstrates that they pay attention to detail, in particular to what you say (so they ask questions, listen, and take notes).
Someone that has a strategy to help you. Driving around showing people homes is not a strategy. Helping you determine your value and priorities and outlining a process is a strategy.
Ask them what sorts of problems they have encountered and how they have dealt with them (can they problem solve). Ask them how many properties they will show you (hint. the answer should be one that shows you they do expect you to be serious and make a decision, once they are showing you homes that meet your needs. )
Lastly I do not see a relationship between the number a transactions that a Realtor has, and their degree of professionalism. I know Realtors with 30 years experience who do not appear to have moved along with the times. I know Realtors with six months of experience that have learned from not only their own experiences, but lean on the experiences of others, and are like a spong. They are not afraid to say "I don't know the answer to that question. Let's find out.".
A Realtor that knows it all may know less than you think. At Keller Williams our philosophy is that we are all "liftetime learners".
I hope this is helpful.
Like the other two agents said, just ask. I provide my resume and background information to any Buyers or Sellers that ask. Plus I post it on my website. Another thing that is important, is that you interview the agent to make sure they have the personality that complements yours. You will be working side-by-side with this person sometimes for many months, and it is important that you can get along.
But may I add IMHO I believe it is the overall ratio and not the total number that should be most important to you. For example, Agent # 1 has only a year in the business, has listed 2 homes per month for a total of 24, and all but 1 sold within the listing period. Agent #2, 6 years in the business, over the last year has listed 40 homes, but 10 of those expired without sales. Agent #1 has less experience but a better batting average.
I don't know if you are looking for an agent currently, but all I am saying is weigh your options carefully. Good luck!