Von Miller's sex tape partner says the NFL star is full of crap -- claiming she NEVER set him up or shook him down ... and says she only kept the X-rated footage as a self-pleasuring aid.
We spoke with Elizabeth Ruiz -- who says Von was the one pushing to record their sexual encounter in Cancun back in June ... and they BOTH shot portions on their own cell phones.
As we previously reported, Von filed legal docs in an effort to block Ruiz from releasing the tape -- and claimed she was trying to extort him for $2.5 MILLION.
Ruiz says the Broncos star is lying through his diamond grillz ... insisting she never asked him for a dollar ... until HIS lawyers made an unsolicited offer.
But Ruiz says the tape was never about getting rich -- it was just about getting off.