I've done these types of deals in both early stages companies AND with early stage products in well established companies. Is the investment really just them investing in taking your product to market as a reseller, or are they giving you cash for product development? Are you treating it like an OEM deal? Resale? Is it an exclusive partnership where they have protected rights to your product for a period of time? Are they improving their own product or position by adding yours or is this a new line of business/revenue for them? How big of a channel do they really have relative to yours? How much is that worth to you? Are there other companies you can approach that might be a better channel or partnership for you? A simple example is on the TV show shark tank. Entrepreneurs often are happy to give up 25% equity or more for a small round of (often fairly meaningless) cash, but access to sell their product through a massive retail channel like QVC or Walmart, where they'll sell to those retailers at wholesale prices but move tremendous volume they would likely never have reached themselves. We're probably not talking about you selling some kind of 'as seen on tv' novelty invention, which makes the situation even more complicated.
So, basically I have lots of questions since every deal like this is unique and there's not a template I can give you to make it successful for you. :)
Happy to give you some more pointed advice if you can give me some more detail/context...