Well, then, it's no wonder you're having trouble selling the product. As a salesperson, you shouldn't be disparaging your own products! Certainly you don't want to lie, but to go around telling prospective customers that your own product is of poor quality is certainly going to kill your sales.
If you want to continue selling these products, you need to figure out what's good about them -- why prospective customers would want
to buy them. If you honestly can't think of a reason why someone would want the product, if you can't think of anything good about it, then perhaps you should look for another job. Find something to sell that you can feel good about.