How many articles are you submitting before moving onto another. I'm using 10 bases for articles and spinning each one 5-6 times so a total of around 60 per product.
If the product converts well then I would keep writing more until you can't take it anymore. Then start outsourcing them.
In my opinion,you should first submit 10 articles.If you see positive results then try to scale up the amount. You should also try to improve the search ranking of the performing articles along with writing new ones.
Cheers. You are definately right. Some products just don't convert but it takes 50-60 articles at least to test the market.