Lacemarket is a second hand clothing sales website that I've been using for years. When they put out a call for UI/UX help I responded and joined the team. Lacemarket was already a fully built and fully featured website and I contribute suggestions for improving the user experience. If it's something simple I deliver a sketch to show the ideal flow and if it involves design changes I create annotated mockups.
Most of the work I have done for the site has been improvements to the selling and relisting flow, browsing listings, and navigation.