What do you think? Has anyone tested this thoroughly?
Not in reality. However, it can only ever be a problem if ALL of the following are true:
1) Purchaser is anonymous. (real life isn't anonymous, since it can be recorded with a video camera)
2) Item is irrevocable/irretrievable. (you could buy a video game license instantly, without risk to the publisher, because it is revocable)
3) Transaction is instant.
As you can see, there are many cases where instant transactions have little/no risk. If all of the above are true in a specific case, however, you better make one of the statements false if you don't want to get burned.