Avast does flag some trainers as viruses. However, the file is not a virus. In ordered to download trainers that avast labels as a virus you have to temporarily turn off your web shield or file shield. I forget which one, it may have even been the network shield but I don't think so. After it downloads you have to unpack in a folder that avast is labeledto ignore. More about it can be found here-
Avast can be overly picky but I use it and simply do what I mentioned above. Hope that helps.