Looks like someone did a really half butt job on it. I wouldn't trust it even with a test fill. the seams look to be too white like the silicone was either done when it was humid out, they didn't let it cure all the way before filling it, or they just didn't know what they are doing.
Big tanks like this I wouldn't take someones word for it especially when it looks this rough. It looks like sections of it are missing or just really thin? Whoever did it next time take some really fine sand paper to get what silicone is left on it after scraping it off with a razor.
I wouldn't trust it as fish room quality even. It just seems like there are too many people trying to make a quick buck off of selling fish tanks and related items I get at least 4 calls a day of someone wanting me to buy something they have. Mainly I would look at the seal between the 2 piece of glass.