when i brough my car off syfon i was on my L's so my dad took it for a test drive, kinda granny'd it again, so then he took it for a spin with us gave is some boot. IMO thats the way to go, if your comfortable in another person driving your car hard then let them, although if i were trying to sell my car i would let them redline it, only if they could prove they could pay the asking price