he did have the right to pull out of the commission (the immature part of me is giggling at the wording), but he didn't have the right to deem how much your work is worth. if the sketch was $3, then pay $3. a buck-fifty is a slap in the face.

and i always have my clients pay upfront before any work is done. i do leave the option of pay-after-the-sketch only if a client seems leery about that. most of my clients are other artists or have done these before, so they don't have a problem with paying first. then it's easier to refund them the proper amount than have them not pay you enough.