Any one have any input on the size of this tank?

Hmm. theres no real comparison in size with another object but it looks like a 10-20g IMO

I'm thinking it's a 20 high.

ask them to measure it...

Definitely get dimensions before buying.

I originally wrote this post saying it looked like it could be a 15 but after some thought and comparing, I'm torn 50/50 between 20H and 29. Ask them to measure anyways though! Attached is a picture of a 20H for reference and you can see how the black frame looks larger in comparison on this picture than in the one you've posted so the entire aquarium could be larger than the picture originally lets on. It could be a 29...

20H: 24"L x 12"W x 16"H
29: 30"L x 12"W x 18"H

Best Regards,
Patrick

20H or 29. As long as it holds water, I'd take it at that price, either of the sizes.

Yeah, looks too tall for a 15, but 20H or 29 would be my guess.

OK...
Judging by the deck its sitting on, assuming its a 2x6 deck board, on a 2x6 joist, I would estimate the tank to be 30x18 which would make it a 29 gal tank.

for $20, I would definately pick it up.