I neglected to include the difficulty of enforcement (train/phone at the time), but if when you sell someone wants a receipt, you are going to be, if only slightly, a little more at risk because the next bloke nay get audited and he produces a receipt from you.
Granted, the risk is tiny, but regardless $500 for a single item that doesn't have an exemption for, say not having up to a reasonable amount of the type of collectable for normal use whether you can prove it is for normal use or not is scummy and shows they may be prepared to use it against the little people when there are far bigger fish to fry.
It's about a culture as opposed to the probability of enforcement... IMHO