To compare to prices on ebay. But you say thats not usually retailed, care to suggest something else?
Pretty much the point with direct sales is that you have products that have some unique features or benefits over competitors that need explaining by a marketing force. They're not trying to compete on price per se, they're trying to provide better
value.
Herbalife for example has their nutrition clubs to provide weightloss support. Nutrilite the fact it's based on organic plant concentrates, Natura it's eco-friendliness etc etc.
And all of course (in theory) offer personal service.
I've noticed when "critics" do price comparisons they often simply go see if they can find some similar product cheaper. That's a ridiculously naive way of evaluating a business. There's probably not a business in the world were you can't find some competitor somewhere selling at least one similar product cheaper.
Price is not the only factor people evaluate in purchasing decisions, or in evaluating "value". The usual approach of the mlm critic implies that virtually every business in the world is somehow a bad proposition because you can usually get something vaguely similar, somewhere, cheaper.
Without having identical products, and ignoring "value added" service, my suggested approach to judging if an MLM product is legitimately priced is to not only look for the cheapest possible competitor, but also for the
most expensive competitor. If people are buying those you then have an idea of the
range of prices people are willing to pay, so it means there's a legitimate market within that price range. For an MLM with more than one product you need to repeat this for a range of products as well, to get an overall view.
Of course you still need to actually look at the products claims, ingredients etc, but simply looking for the cheapest
might be competitor is not a legitimate approach.