Great topic with lot of useful information ; one problem is seasonal business and the vagaries that go with it . They probably did not see big $$s in your repair when they had other big $$ work to do [ which they should have told you rather than the brush off you got with your engine being " shot " , how did they determine that ? ]
#1 compression , my lesson was do not use the automotive type with the hose ,it gives a false low reading use the type that screws directly into the block : An engine with good compression is not " shot "
#2 Fuel problems can be related to ethanol mixed gas ; I pay more with high test ethanol free but they Yamaha dealer told me to still add their fuel additive to my fuel ?
#3 I agree with DIY if you can but get a service manual ; a little late but the manual does show you how to test for a fuel pump !
#4 Not your problem ? yet but every older OMC engine with a problem try and run it in the dark if you can : did this and saw an intermittent spark near the power pack ; the bolt holding the power pack was starting to back off because of the shaking off a 2 cycle engine so I was loosing intermittent ground ; turning a wrench may have saved my a " $ 320 " repair !
#5 Not your problem ? yet but check for a partially blocked exhaust . A good mechanic could not diagnose my problem ; he called OMC nd they advised him he had done everything else that was the problem !