This tool is a real treasure, especially for thrifters. Based on recent(ish) experiences, though, it seems like using it should be more straight forward than it is.
1) Do not add a WANT entry for some parts below a HAVE entry for those same parts -- contact the person with the parts directly first! Do you expect the HAVEr to note the new entry and come after you to ask you if you really want the parts? That seems unreasonable.
2) Less necessary, perhaps, but maybe if you have new parts, you could scan the entries for that game and contact those that need them directly before you add them to the list?
3) If you list that you HAVE parts, pretty please, respond to people inquiring about them. Otherwise, what's the point of listing them?