I only invest on BLC these days. I use a machine learning system (the results of which are publicly available) to filter out loans with reasonable rates of success and then I personally scrutinise those loans. It takes time to work out the tell-tale signs of a scammer and the signs vary depending on the type of scammer (incompetent individual, scammer individual or group of scammers).
That is what I feel. These lending sites just take too much work and effort to avoid the scammers for the meager gains you can make. Frankly I think BTCjam likes the scammers and they probably only really care about collecting their up-front loan fee. They sure don't make it easy for the lenders.