I see people giving free landing page, product reviews, etc. all the time (and have benefited from a lot of these) and so thought I'd pay it back.
If you have an MVP and no customers yet, post your link in the comments.
I'll sign up for your product, try it out, and give you my honest review.
Obviously I won't be in the target market for every product but I could maybe help with UI/UX, copy, onboarding, and anything else product related.