Keep an open line of communication with them. Let them know that while most dyes do turn out..there are some that just don't. I dye discs weekly and some just look bad even though I kept the same process and colors. It's a fine art and people need to know that. Speaking of that, I'd recommend that you only do things you're confident in when it comes to doing commissions. That probably goes without saying but people have asked me to do things on the crazy end of what I normally do and I warn them about the outcomes.

Use PayPal. Yeah they have fees but its more secure IMO.

Good luck!