Granted, it's some easy money, logging it in & then logging it out, but it's still the FFL whom the BATFE will be questioning, not you.
It's not always easy. I've had transfer-only customers who were far more high-maintenance than any regular customer.
Some will track the package online, and the second it says "out for delivery," they start calling every five minutes, asking if it's there yet. They're at the desk the second the UPS/FedEx truck pulls up, and no matter how busy the store is, they expect it to be checked in
right now, to the exclusion of anything else.
Then they'll argue that the gun is only in 88% condition as opposed to the 90% condition the seller claimed it was. These people literally bring magnifying glasses. They'll make the clerk stand there for 30 minutes while they go over the gun and complain. If there's a discrepancy in condition, they yell at the store clerk rather than the person they bought it from. Sometimes, they'll demand compensation from the store.
I lost track of how many times I had to explain, "you didn't buy it from us. You need to take it up with onlin3sh00ter44."
Sometimes, they'll try to blame the shop. I had one guy scream profanities at me, swearing that someone at the store had taken the gun and shot it before he got there, because there's no way a new revolver could possibly have powder residue in the barrel (they test-fire them at the factory, fella).
Then there are the folks who will call dealers who may have the shop's FFL on file and order guns without the FFL's knowledge, claiming they've already cleared it with the shop.
Often, those are guns the shop had in stock.
Then there's the fun situation where they get denied on the background check, and the shop has to make arrangements for return shipping after getting chewed out by the customer for 45 minutes.
As far as opening the box, if you can be there shortly after it arrives, it's a reasonable request that the dealer wait. However, if eight hours have passed, and it's time to close up, the gun has to get logged in, and it's going to get opened.
That doesn't mean it's getting drooled on or fondled. Usually, the firearm doesn't have to be taken out of the plastic wrapping. The dealer does have to be absolutely sure of the serial #, though.
You do get alot of orphans, with no indication of why they were shipped, or who they were shipped for.