Double spent transactions will be tagged as "Double spent" like this x spent the same outputs as y something from block explorers so you can easily identify it and as you can see its not. The miner fee included is just too low making the transaction stucked so honestly he doesn't have the right to call you a scammer as he included a low fee moreover unconfirmed transactions can't be trusted so you have every reason not to send the riot points until confirmation comes.

With that fee i doubt it will ever get confirmed so I quequed your transaction on antpool. It should be confirmed within a few hours.

Sadly,  you would be a scammer to sell to someone else unless you have multiple as its likely that this transaction will go through.  It's just a matter of when,  and it may be a good while.  The good news is that in the time it's taken me to type this,  it may have confirmed on its own.

I'm not sure if it's a double spend,  but tell him to increase the fee if possible by right clicking the transaction on his wallet and pressing increase fee.