Advice on client priority/stalled payments

[jesskat.livejournal.com]

This is not a beware warning, I'm just looking for some advice/opinions.

If you have a number of people lined up for a commission and the one at the top of the list keeps stalling on payment, how long is it appropriate to wait until moving on to the next person?

I was recently in contact with a client who first seemed excited about me getting started on their commish as soon as possible. Once I was ready, I sent them an e-mail to inform them that I would begin work on the sketch as soon as I received notification of payment from PayPal. They were usually quick to reply, but this time it took them a bit longer (granted, only a week, nothing worth panicking over). I sent them another e-mail to make sure my previous message had been received and they replied again within a few days, so all is well now.

I'm only asking because it made me wonder what to do should a similar situation arise in the future, one where contact was lost for much longer. It made me consider the possibility that some commissioners might at first seem eager for a pic, but as soon as the issue of payment comes up, they might get cold feet and decide to retreat without a word to the artist.

I like to work off my commissions in order of first-come-first-serve. I also never accept payment until I can guarantee I have the time and energy to dedicate to the piece in question. So I never take money from more than one client at the same time in order to ensure that I don't keep people waiting for months for something they've already paid for. I wouldn't have felt comfortable moving on to the second person on the list only to have the first person pop up again after a month of silence, saying: "Here's the money! Now you can start working on my pic!" In that case I wouldn't know which person should be my #1 priority: the person who kept delaying payment but who technically came first, or the second person who had waited patiently long enough and whose pic I was now working on.

In this scenario, what would sound fair to you? That I finish off the second person's commission because they were quicker about payment and politely explain the situation to the first commissioner, OR apologize to the second commissioner and tell them I'd have to put their pic on hold while I finish off the first person's pic because we had an earlier agreement?

In this case it was only an issue of a couple of days, but I would hate to keep people waiting for months just because of one client who may or may not have gotten cold feet and disappeared without a trace. How long is it fair to wait until moving on to the next client? And should client number one pop up again with payment and demanding their share of the trade, what would the appropriate response be? In general, if a client takes an unreasonable time to come up with payment, how far down the list should I move them? In case months had passed, would placing them at the end of the queue seem unreasonable in favor of all the other people who had been kept waiting?

(I hope this wasn't too long-winded. If the mods want me to cut this, let me know.)