Current tenant want to buy my condo

My current tenant wants to buy the condo I have been renting to him for the last 4 years. He says he has pre qualified for a mortgage loan. I believe the condo is worth around $135K.  He has offered 125K with the seller, me, paying all closing cost. I own this condo outright, no mortgage. There is a real estate agent that just bought a condo in the building last year and I have asked him if he could help with the paperwork and closing (for a fee not set yet). Or should I just contact a Title company? I need advise on the best way to handle this transaction. Just fyi, I love this historic condo, but slowing down and tired of the renting hassle.