[ Marty never really liked to bring up Hill Valley when it came to careers, or anything like that. Especially not when it came to his friend. With Doc's reputation and how long it stuck around, Marty had no doubt that accusations of him burning down his house, or building death rays or whatever probably stung him a bit. Not to mention waned his confidence.

Seeing Doc doubting himself was kind of scary, to be honest. Marty's smile fades, and he puts a hand on his friend's shoulder. ]

That's 'cause the people here know something great when the see it, Doc. Look at all the stuff you've made! [ He points to what his friend has to offer, the smile coming back. ] And a time machine, too! That's heavy duty, Doc.