I tend to think of the following as bad signs:
1. They don't specify the steel. If it's some generic "hand forged hand folded high carbon steel," steer clear. You want to KNOW the exact type and grade of steel. Avoid 440 or any stainless swords at all costs. Stainless is NOT a good thing in swords. Avoid "damascus" swords UNLESS they can tell you what steels went into the making AND the HT numbers. The heat treat is the most important aspect of any blade. If they won't even tell you the steel they used, it's often because they don't know.
2. They don't specify the HT numbers. If it's differentially tempered, they should reveal the edge and spine (H)RC numbers. If they don't, you can assume the QC isn't up to an advertised guarantee of the numbers, and the heat treat isn't good enough for you to feel safe.
3. Made In China/Pakistan/India. This isn't necessarily an automatic bad. There are some good swords that come out of China, at least. But you want to be very sure of the provenance. Points 1 and 2 are critical here.
What is your budget, and what do you plan on doing with the sword? If you plan on using it for more than decor or doing the occasional pool noodle/water bottle cut in the backyard, what's your training background look like?