Oh man I have this happen all of the time. Some of them are even so in the way/in your face that my buyers are turned off by it. More so when the home is sort of small, when you have 5 people now treading around in the same room, the room will look even tinier and feel very crowded.
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.