OK, the things I have learned about purchasing.
1. They often will not respond. If it seems super cheap, it is likely just put up to test how many players will offer. You might get lucky but most likely not.
2. Look for how long an item has been on the market. If it is 1+ hours then you are much more likely to get a response, as the item has hit its price point.
3. Sometimes items do not readily get removed from the market even after the exchange. This is why a 1+ hour window helps to get around that.
4. You can direct message the person just to see if it sold already.
5. If an item appears to be going cheap, make a higher offer. Sometimes that will get a response.
Its a stupid system that makes for a tedious part of the game that should not exist in today's programming.