How is commissioning out-of-game art with sapphires typically handled?

I've ordered a lot of in-game commissions in AJ, and 90% of the time I paid for the masterpiece after it was done. I don't know what's the usual for Out Of Game ones though?

I'm intending on ordering a bunch of random commissions once i finish my ref sheets on my toyhouse. But i really don't want to be scammed or have the artist be worried I'll scam them...

So I guess if anyone can explain how their experiences went or what I should look out for, it'd be appreciated :3