incrediBILL - 5:14 pm on Nov 4, 2012 (gmt 0)
The easiest way to sidestep this is to only put unique part #s online and don't use those from the original manufacturer so nobody can claim they're the same thing, like the mattress industry does.
Comparison shopping sites also go right out the window.
FWIW, I think if retailers don't opt-in for this that if money is deducted for price matching without consent they'll simply stop taking PayPal. The thing I'd really worry about is if this proves popular that Visa, MC and Amex follow suit.