Yeah, I did it at mine. We didn't have the DVD's printed yet, but we took pre-orders and sold them an empty case, then mailed the actual disc when they were ready a couple of weeks later. Was good, we sold a few hundred. It's also really nice to see people buy your movie after just having paid to see it. Plus you can sign it for them.
What do I know? I'm a bear. I suck the heads off of fish.

OK. I may consider this. Thank you.

I can't remember who the filmmaker was, but there was someone who did this like 10 years ago, and him selling copies, is what actually got the movie a distribution deal cause the right person came along and bought a copy, and that spread the movie around, and got a distribution deal after. So maybe it's a good thing in that case?

You selling DVDs in the lobby should not affect acceptance in any festivals or any future distribution deal.