There is a guide line for negative ratings, we are supposed to give negative ratings when the person doesn't pay, steals, damages your town or uses a really abusing language I think. Not for taking long time, not replying, cancelling the trade or silly stuff like that. So no, I've have never given a bad rating, I was tempted once when a little one came to my town and started running everywhere but I preferred to kick him out instead and gave him a warning, it was okay after that.
I almost got a negative rating in two occasions. Once I was following the host quietly as usual but the game froze and you know what it looks like, the character stops and then is suddenly a mile away (not that much...) a split of second later and it gave the impression to my host that I was running :'( I wasn't....I swear!
The other time I was selling things in another town and my pocket was full so I let bags of money on the ground and made place, when the host saved I quickly picked up my money bag left on the ground that I was forgetting and the host thought I had stolen his peaches! I asked him to count his peaches and see if there were some missing, I knew I didn't take any though, even offering him to give him 3 baskets of perfect peaches if he wasn't believing me...He finally let it go, but I'm sure he still think I stole his peaches. OTL
I felt quite bad about it, I was behaving as always and was wrongly accused of acts I didn't do. Well I got a neutral rating but it let a bitter taste in my mouth. Although it just a game, I shouldn't care that much about it.