regular gas + octane booster= ? RON

Jordo!

Uh, a bottle of octane booster isn't going to do much, which is the whole point.

You're better off demanding to accompany them on the journey to the gas pump if you are that worried.

Or tell them not to bother filling it up -- you'll do that.

Failing that, if you are that concerned, drive around at fairly low revs, putting very little load on the engine (less load means less torque produced, means less likely to autoignite -- although it is certainly possible to knock even at idle), get through a 1/4 or 1/2 tank of gas and then top off with high test.

Or break out the siphon hose and start sucking

The message I'm getting from people on here is that they don't trust car dealers as far as they can throw them (fair enough) but they DO trust snake oil salesmen selling unregulated, mystery fuel additives (why?).

__________________
Enjoy it. Destroy it.