Sean Taylor is the act of lowballing for something with great value, informing them that it's not worth much, then re-selling for 10x the value.
Mike: Bro I just Sean Taylor'd my friend for the GT Venom
John: Oh shit really? How much did you offer?
Mike: $20, I convinced him it wasn't worth much.
John: Nice! How much are you gonna sell it for?
Mike: I think $2,000 is fair :)