I don't entirely like the markup you have for the MarketPress shortcodes. Well, sometimes its just the style that I don't like and overriding EVERYTHING is such a pain. It would be nice if there was a way to write my own plugin which could register new code to _render_ a result (say for [mp_list_products]).
Minimally, I'd like to see all the shortcodes get a class attribute which would default to some value (not empty). this way the default CSS could be overridden relatively easily, by giving a new class name, and the default would not interfere.
Ex, right now [mp_list_products] renders <section id="mp-products" class="hfeed mp_products mp_products-list">. If it rendered <section id="mp-products" class="hfeed mp_products mp_products-list mp_products-default"> and [mp_list_products class="foo"] rendered <section id="mp-products" class="hfeed mp_products mp_products-list foo"> and your selectors that now start with .mp_products started with .mp_products.mp_products-default, I could do almost everything I need easily. I could use the style .mp-products.foo and it would NOT have any style from the default (which is what I want in my case)