"they won't try to sell you something unless the components you have are incompatible"
"they won't try to sell you something if the components you have are incompatible"
Don't pretend that these are not opposite statements. I would expect that most of us would favor not being sold incompatible components. I'll step away from this debate about basic use of language. Golly, I don't need no wrong parts!...or is it wrong parts that I don't need!