Regarding bluffing: I've seen it happen where the company has asked for a pay stub as part of the final paperwork to confirm that the stated current salary was legit. So yeah that could be a downside to bluffing if you want the job.
(It just occurred to me that if there was "an app for that" in this case, no parent would ever be able to trust their child's report card again.)
Make it look more or less like the original. As long as nobody sees the original next to the mock-up, who's ever going to notice that one or two digits changed?
Regarding gossip, "Would you trust a company who checks up on someone's previous paycheck?" seems to quell that pretty quickly.