even if it was a cube, 48L x 48w x 30h, that would only be 300 gallons.
Now if it was 72" long, which it very could be just by looking at the decor on the top and the rail behind the tank
it would have to be 72 x 36 x 30 like Bderic said. that would be 336 gallon then minus the overflow area.
I dont think its a 325. But with the center overflow, hard to say how wide it is.
I would guess its a 48x30x30 making it only a 187 gallon, but thats only looking at the pic. Hard to tell.
did you email him and ask him the L x W x H yet???
If it was a 325, that would be a great price. Id event like to have it if it was. But would have to be a wide tank for me to even make that trip to pick it up.