The first used gun I ever bought was online, from Gunbroker. It was an H&R 732 and it was used and abused. Two of the cylinders were out of timing and wouldn't lock up fully. I contacted the seller and requested a refund, which was given.
I decided then that older, questionable, out of production, used revolvers weren't worth dealing with online and are relegated to in person dealings.
Now, I just picked up a used Heritage .32 H&R Mag single action revolver I got off gunbroker and it's great. Thus, I'm of the opinion that it depends on what seller you buy from and what type of gun you buy.
You really have to trust your instinct with used guns. The best thing you can do is handle them yourself in person before you commit to buying them. For online purchases, buy from reputable dealers who have a high rating that aren't the busiest sellers on gunbroker. The busier the seller, the more chances they will make a mistake.