I used to get delayed every time when the instant check was Federal. Now Oregon has their own instant check system and I've had no problems. Of course the OSP charges $10 each time.
Years ago a delay cost me, because of a jerk at a gun shop. I was in a shop about an hour away and overheard the son of the owner trying his best to sell an old 10/22 to a customer, knocking the price down to $85. The guy left without buying it, so I asked if he would sell it to me for that price.
He agreed, I started the paperwork, he says "Oh, you'll need a magazine with it" and starts taking a new mag out of it's package off the wall. I told him I had a couple mags already from my old 10/22 that got stolen, so he agreed to keep the mag and knock another $10 off.
I was delayed but was going to pay for it anyway and pick it up later. He said just pay for it when I pick it up and stupidly I agreed.
I called a couple days later and asked the owner if it was OK to come pick it up yet. He say "sure, no problem. This was the one you did some trading on, right?"
I say "no, just a cash deal."
"No, that can't be. We can't sell it that cheap, that's below our cost"
"Sorry, I don't know about that, but it's the deal your son made."
He didn't say much more but when I got there he says my paperwork was lost and if I wanted the rifle I would have to fill out a new 4473 and pay his price.
Not a good way to do business.