First off, this is a neat project. I don't buy hardware often, but I think your idea creates value here (and could be applied to other industries too).

I think sharing some of your metrics with us should influence the advice. There is a lot of advice in this thread, but I don't know that it's good advice.

- How long are your users staying on the site for a typical session?

- How many (monthly) actively users do you have? Do users return or really just come once?

- Where do your users come from? (traffic source)

- What are the typical price ranges your users search for?

- What kind of parts bring in the most revenue?

- etc.

Essentially I think you should put together the answers to the most common questions an investor would ask for a seed stage pitch deck.