From what I've seen that's not an unusual price for a used tank where you're at, but:
Do you know the exact dimensions? It may be smaller or larger. I commonly see 125g advertised as 100g, but I also commonly see 90g or smaller advertised as the same, and even a couple of 55g.
Have you seen this tank? The stand may not even be a stand or be in bad shape, the tank may be in bad shape or even damaged (even if it's currently set up).
You don't know anything about the equipment or fish. The fish may be something you'll have trouble pawning off on a pet store (such as a large pacu) or something that won't really get you store credit, so they may not benefit you at all.
The filters could simply be powerheads and a UGF, or some really cheap worthless HOB. Again, something that doesn't necessarily benefit you at all, so their inclusion with the tank can be ignored.
Decor could be anything.
So all you know currently is that you have a possible tank+stand+top (and maybe lights, it wasn't mentioned) that is claimed to be 100g. It could be a good deal, or it could be a bust. I wouldn't commit myself until I had more info. Even if you gain all the info and you go over there and it isn't what you want don't be afraid to pass.