I went to a customers house to clean his flue last week, he said he had it cleaned last year but he only had one fire since because it smoked up his house so bad. I asked all the normal questions thinking he had a pressure problem, then I got on the roof and this is what I found. The other so-called chimney sweep didn't get on the roof, cleaned it with a viper and called it good. That is why it is always a good idea to get on the roof if at all possible.