Is this a really weird crypto scam?

I had two customers today who wanted runescape gold and they wanted to pay me with crypto, they didn't want to pay with anything else. I have the crypto as an option but then again I'm not so experienced with it, I use coinbase to accept such payments because it's very user friendly.

In both of the cases they send the money to my coinbase wallet and it appeared in my email that I received bitcoins, however the transaction was pending and it said that it's invalid and I never got the coins.

Both of these buyers pressured me a lot and one of them was even threatening me that If I don't deliver him the gold then he will get me banned because he said that the amount he send was non-refundable and that he saw clearly that I received the coins.
Now, this is really irritating and I'm thinking to remove coinbase from my payment methods.

Are these people trying to fake "sent payments" so that you deliver them the goods then they somehow cancel the payment? has anyone else seen something like this?