Ask them what makes them better that any other Realtor?
Ask them to give you a CMA and just get a general feeling if they are trustworthy. interview 4-5 agents they see what is the difference in price they recommend you list your property for. Some Realtor will tell you your home is worth more than it really is just to get the listing.

The key to selling your home faster is to price it just right. An over price home will take longer to sell.

The commission is negotiable but if it is too low (4% 2% for seller 2% for buyer) you won't get a lot of showings. Some Realtors will not show anything under 5% (2 1/2 - 2 1/2 split)