I have even had sellers point out nothing but the negatives to my buyers before!
I have no problem letting my sellers know this when it is my own listing, however sometimes the listings are not mine, and I bring in the buyer, which makes telling the seller to back off a little more---- difficult.
I guess I kind of have to suck it up, and just try to point out the positives the home offers and hope that my buyers like it.
90% of the time though, my buyers buy a house that they have viewed that was either vacant, or the sellers just let me do my job and stood outside or in the living room during the showing.
Best of Luck,