On a 1996 Formula with 502 mpi's, would ya'll get a pre-purchase inspection including compression test etc from a reputable performance boat dealer or a marine survey and still have to go get a compression test?

I wouldn't take anyone's word for it, not in this Biz............you'll have to get a survey for insurance purposes anyway, up to you to do the mechanical.....

Call Ed Cozzi 954-895-4633
He has done many surveys for me & has been around for many many years,

The survey may include a compression test. The last one I got done included the CT.