Of course it pisses them off, because they know if the fence is falling over, and yes, they've factored it into their price. It's not news to them. To change people's minds usually requires some revelation.Giving reasons for a lower offer is Ok, eg if there are repairs needed like a fence is obviously falling over or front stairs unsafe. Though they may have already factored it into the price.
"That falling-over fence you have is falling over, and as such will cost me money to make it not-falling-over" is not a revelation.