This may seem like an odd question but you may want to start asking it.
I say this because there are many Realtors that simply like to dabble in Real Estate; it's something to keep them occupied. This is a status that you as a client should want to be told up-front, but you won't know unless you ask.
I would not want to go to a part-time professional for any service. My reason is this is a fast paced business with new rules and legislation along with new technology happening all the time. If you only do 5 or 6 real estate transactions a year your skills could become a little dull as compared to the person completing 25 to 50 transactions a year. We all know that the more we do, the better our skills become. The best and most successful are on the "field of competition" everyday they are definitely not "part-timers".