See if they're willing to advertise on consignment if they can't purchase your rare books. If not then try https://comics.ha.com/. Make sure you know how much your collection is worth before attempting to sell it.

Condition is everything.

You'll get the most for your money on eBay, but that takes time, patience, and knowledge. I'm a member of a few private groups on Facebook that have serious collectors where you can sell with confidence. Your local shop is certainly a good start, too, but you won't make as much as online.

You need to fine someone you can trust to look at your collection. They will know what is actually worth money. And, as already said, the condition of the books is vital.

I also would be happy to help you get a general vibe if you shared some of what you have. Even if you gave the titles of the comics if you have runs, and we could let you know the ones in those runs that go for the most.