make it worth my while

Kmart has been running ads recently stating:

"If you find a cheaper price, we'll match it"

Ok. So I've been shopping around for and have found a place that sells x for $100.
If I decide to not buy it from this store, and instead go all the way back to Kmart, they will lower their price to match it. Not make it cheaper. Match it.

Now why the hell would I bother doing that? Make it worth my while! Give me another 5-10% off. Give me a $10 gift voucher. Offer to polish my bloody shoes. Something!

Step up or fuck off. Cheap bastards.