According to claims made on this thread there is a bug currently in existence in LSL related to llSetPayPrice which allows the exploitation of vendors. Apparently the details are only known by the makers of JEVN vendors, and no further information is forthcoming from them, but we are also told that it is fairly well-known.
This bug, we are told, is not the usual "changing the displayed item can result in a different item being bought" one, which is already known.
1. Is there such a bug?
2. If so, what is it?
3. If the answer to question 2 is not judged to be something that should be released publicly, how can scripters of vendors avoid it?