It's rare, but you're wrong here! I've seen fake transactions on Blockchain.info (now Blockchain.com) years ago, they were used by scammers to pretend they sent funds. Those fake txids didn't show up on any other block explorer.
I never found out how they did it, but judging by this topic, it's still possible.

General advice: NEVER accept an unconfirmed transaction as payment (unless you trust the source completely), and don't rely on blockchain.com (they have many bugs).

You can only Merit a user after you've earned at least 2 Merit yourself.

Chances are you got scammed