$50 is damn expensive pizza and beer.
12-pack of craft beer - $15
Pizza, wings, delivery/tip - $35
We're talking about this person asking a favor of someone to help them save $1500+, by giving up a morning or afternoon to teach them how to do the job (that they wouldn't be able to DIY). $50 on food and beer that you'll split with them doesn't seem bad to me; if someone asked me to come over and teach them how to do a brake job and then offered me a $5 carryout Lil Caesars pizza and a Bud Light tallboy, I'd be gracious, but offended. I likely would also decline any future requests from this person.
It's a little different than me chatting with one of my buddies about weekend plans, where I mention I was planning on a brake job, and they volunteer to come over and help because they haven't got anything else going on; you were going to do it yourself anyway, but you've got the extra hand as a benefit. Those are situations where splitting a 6er of Yuengling and hot dogs on the grill are appropriate (you get what I was planning on cooking myself after finishing).
If the food/beer barter system isn't on par for services performed, that offer is no longer valid. Moving forward, only cash payments will be accepted.