Take it from someone who has done more commissions than all the people here combined: I've been doing this for over thirty years and I still have yet to have one complaint about the work I've done for my customers. Most recently, I have a customer who keeps telling me that he will pay me for my work, but he doesn't have the money. I just keep getting the same old tired excuses. Now I have to sell to recover my labor and my material costs. I seriously doubt that anyone will pay me for what I've done at full cost on ebay, or even these forums. I'm going to offer it for the full price on here, but I don't think anyone will want something I made for another person at full value even though everything is brand new. I guarantee the quality of all my stuff to 100% customer satisfaction, or their money back (if they return the item in its' original condition). I don't think for all the work I've done on all the stuff I've made that my prices are any higher than anyone elses. I tried to sell it over on hobbytalk, but everyone there looks at what I'm selling, then goes on to the next thread! I sometimes wonder if it's even worth the aggravation?
It all depends on your customer, or the situation surrounding what you both decide to build. If you want to do commission (I don't know why anyone would want to) - you can advertise what you've done in the past and if people like it, they'll ask you to build for them depending on the person and the difficulty of the build. Sometimes you'll wonder what you've gotten yourself in to if it's too involved, and if you're not familiar with the subject (references). It's all up to you to decide what you want to do. Just keep in mind that just because you'd like to do something, it doesn't always meet your expectations of you think it should. A lot of transactions go wrong ALL THE TIME!!! Don't be impressed by seeing others doing this - it isn't always what it seems to be. It's just like any other transaction via technological means rather than being done in person - you don't always know who it is that you're working for, or whether or not they'll try to get something for nothing, or their lifestyle changes for the worst and then they can't keep their end of the bargain. I'm at a loss for words for the latest guy - I feel sorry that he went through a divorce, but that's not my fault - I just built his stuff, and painted it and made some weapons for it. Now I can't get a single cent for any of it - what's really sad is, I didn't charge him nearly what I would've normally - and I still can't get anything for it!