I have seen and have had that complaint myself.
When some of the guys place an ad I guess they figure they can take their sweet ass time to reply, but it's just not here that I see it.
It happens on ebay a lot as well.
If I do not get a response within a couple of days I look elsewhere and then when I do get a response I let them know what I think of their I'll get to it when I feel like attitude and that I just spent more $ elsewhere. That usually fries their bacon.