According to the e-commerce site, someone scooped up the guitar -- which was featured in a viral video at the end of September -- on Tuesday evening for a whopping $6,550 ... even amid doubts about the guitar's authenticity.

As TMZ previously reported ... Gary Estes, a Texas resident, spent $4,000 at a charity auction on a guitar advertised as bearing a Taylor Swift signature on it. Upon receiving the guitar at the auction, Gary was also handed a hammer ... and proceeded to smash it up.

The video soon went viral on social media ... with Gary later stating he didn't have any malicious intentions with the bit, claiming he was just joking around.

Gary clearly didn't feel too attached to his $4,000 destroyed guitar ... the eBay seller noted the man donated it back to the nonprofit ... the Ellis County Wild Game Dinner. The money from the sale will reportedly be used to support agricultural education for local youth.

While the listing advertised the guitar as one "autographed" by Taylor, a source close to Taylor's merch company denied the claim ... doubling down and clarifying the pop star did not sign the guitar -- it was later determined Tay's signature on a separate item of memorabilia had been attached to the instrument.

Even though the listing included a "certificate of authenticity," her merch company is not the one that provided the documentation, as it's not an official Taylor Swift guitar.

There's other questionable things about the certificate ... especially since it doesn't have a seal, something that's typically found on documents like this.

Regardless, it seems someone was still interested in the eyebrow-raising item ... as it's set to ship to a new home.