I've touched on this before, but I need to go back to it. MAKE PAYING EASY. Whether you only accept money orders or you can process credit cards online (best), make it pain free for your buyer to pay you.
Nobody wants to go through any hassle to GIVE someone else there money. So what I would say is simplify the process and accept credit cards online. You may be charged a fee, but it's worth it in the long run. You will get money faster, safer and people will be more likely to come back to you.