Gabe, a good question,
Let me add another point element that may be of help. Keep in mind, this issue is a NEGOTIATION and should be approached as such. If these folks are truly wanting to sell. then that is the outcome they are seeking. Keep that at the top of everyone's goal.
Feedback for other real estate professionals is not worth the time or paper it appears on in the eyes of the seller. They already know the results will be...."REDUCE THE PRICE!" Using peer feedback may result in the doorway to negotiation being nailed tightly shut.
Consider one of the following:
1. Place a prominent display in home with the banner.."I NEED YOUR HELP' and ask the visiting buyer, not the agent, to anonymously provide feedback regarding the home. Items such as, curb appeal, condition, size, upgrades, and landscaping should be there. Then slip in OTHER: ________. By not steering the visitor into a specific comment, what is volunteered will possess true relevance.
2. Open House - use same tactic as in Number 1. This is a great time in query your Open House visitors regarding how they go about their home search.
Finally, advise the homeowner, "Investors LOVE stinky homes. Why? Buyers don't want them." Investors will discount their offer 40%. Be aware, the damage is already done, all you are doing is allowing the home owner to come to your side of the negotiation equation.
Best of success.