What is a good 7 day retention rate after signing up for a social shopping startup?

A 7 day retention rate may not be the right cycle by which to measure, depending on the natural usage patterns of your users. And besides which, this is probably not the one metric that matters to you, right now.

For example, are the core social components working well but there's little evidence of any purchase conversion? Or is it flipped? People are reacting to certain purchase opportunities but not contributing too much to the social community you're trying to build?

To be clear, retention matters *a lot* to the long term viability of your business, but it's not something to overly optimize before getting the core of your product tuned to what people want. So focus first on measuring the extent to which the actions you want your users to do are getting done before looking at overall user retention would be my suggestion.

Happy to talk through this in more detail with you.