Just use a smart phone and the Amazon app. But thrift stores aren’t the best places to get books. You should find places to buy them in bulk. Generally, I give 3/4 of my books to thrift stores because they are better for local sales than online. I feel sorry for the people who try to scan or eyeball those books then resell them online. I’ve given many books that look like they’d be worth something online to many experienced eyes. I’ve even been at one thrift store when an “experienced” online book seller thought they hit the jackpot with my discarded books. I tried to tell him, but he didn’t listen. I’ve also received many books that looked worthless that were not.
When I buy in bulk, I’ll scan a few items until I get to a point where I know I can offer a reasonable figure. I almost always give more money than other book sellers are willing to when buying in bulk and that pays off because I get more referrals. And some of those referrals lead to many more books offered for just the price of gas to come and get them.