Hi Puss.
I've stopped at loads of hotels and like you, have been happy with them, only to find, later on, negative reviews.
One thing a hotel owner did say to me, was that some of the reviews are bogus - rival hoteliers or their staff posting bad reviews for obvious reasons. Whether this is true or not, I don't know.
Apparently, according to this chap, you don't have to have actually stayed at the hotel to submit a review on TA. After speaking to this chap, I have to say I'm rather suspicious of some of what I read now.