Q:  My A&P/IA says that a previous STC installed in my airplane precludes incorporating your STC.  What now?

A:  This would be a very unusual situation.  However, should none of the "authorized persons" be willing to sign your 337, your investment is safe.  100% of your purchase price will be refunded, given that you return all documents along with a written explanation of why the STC could not be incorporated, within 60 days of purchase.