A friend of mine has been studying chipping claims for a couple of years for his C230K Benz, and he finally found a place that sounded like it knew what it was doing (after saying no at 10+ places). He got the work done, and felt "some" difference.

Luckily he got his car tested on a Dyno Dynamics rolling road before he got the work done. So he went back for comparison.

The power claim was for 25hp more - the truth was 5hp.
The torque claim was for quite a bit, the result was 10 foot pounds.

Had the chip removed, and received a full refund.