Here's the thing, though, the six-figure check is very real ... and Dog could cash it, but then he'd really be screwed. His literary agent, Alan Nevins at Renaissance Talent, tells us the dough was delivered Wednesday morning to his office by FedEx, and it immediately set off all sorts of alarms.

We're told this all started last month when Alan got an email, seemingly from the office of Sheikh Mansour bin Zayed Al Nahyan -- the real Deputy Prime Minister of United Arab Emirates -- offering to pay Dog a handsome fee to speak at an economic empowerment convention for small business owners on August 31.

They sent a contract that was very sophisticated -- with all the proper clauses regarding travel, taxes and indemnity -- so both sides agreed to follow up and see where it all led. Dog joked to Alan that if it turned out to be fake, maybe he could help break up a money laundering scheme.

Sure enough ... things got sketchy after they negotiated a fee and signed the deal. First off, all communication was by email -- the foundation claimed that was due to the 11-hour time difference between L.A. to UAE.

Then there's the website for the alleged event -- mansourfoundation.org -- which looks very real, and even allows you to make donations. However, only by snail mail or email ... NO credit cards. Alan thought that was weird and tells us he called the host hotel listed on the website, only to find out no such event was going down there.

Another red flag came when organizers in "Dubai" told Alan they'd had trouble wiring funds to the bank where he has his business account, so they asked for his personal account at a different bank.

Dog and Alan knew it wasn't real at that point, and decided to walk away -- but lo and behold the live check arrived. The catch was organizers asked Dog to donate $250k of the funds back to the organization.

Alan says he did some research, calling the Portland bank that issued the check and the Portland construction company -- Benson Industries -- that allegedly wrote it. Both are real! Alan says the bank confirmed it's an active account, but wouldn't say for whom. Benson told him they had no knowledge of any such check being cut.

Federal and local law enforcement sources tell us this scam is like the new Nigerian Prince letter ... except with much higher dollar amounts to target rich celebs. We're told, a rash of celebs have been hit up lately -- and if Dog had deposited the check, the funds would have vanished a few days later. So, if he'd sent back the $250k, it would've come out of his own pocket.