The most common complaint I found from when I when I owned an estate agency went like this:
EA - Your house is worth ?x
HO - I want ?x + y
EA - We have an offer for your house at ?x
HO - That was quick it must be worth atleast ?x +y + z then, tell them we will accept that and put the price up.
EA - The buyer has dropped out
HO - Annoyed, why aren't you getting any interest in my house!
To know whether this is a problem, more understanding of the reasons for complaints would be needed.
I suspect that many are about differences of opinion over the value of the house, and that is, in fact, understandable.
Looking at local houses on the market, most are priced very high for today's market, often at not much less than the peak. That is either poor advice from the agents, or people pushing for too much. If the former, that is good cause for complaint, if the latter, then not really the agents fault.