Car repair manuals

My husband has about a dozen car repair manuals from the late '50’s to the '70’s. He would like to sell them - 1 - are they worth selling?; 2 - how should we price them?
Thanks for your help.

Visit a classic car swap meet, set up a portable table, spread the books out, and relax in a lawn chair with shade umbrella. Offer the best at $10 $5, some more at $7.50 $3, and the rest at $5 $1 at the beginning of the day. Mark the remainders down to $1 50¢ at the end of the day. You will sell them all.

Mazel tov!

I've decided to mark them down a little. You will sell out by 1:00PM.