Discounted Gift Cards Website

I recently discovered the website plasticjungle.com.
I think this will be a great website to remember when my boyfriend and I do some work around the house this upcoming summer. From reviews, it is a website that you can sell gift cards on to receive some cash back, and the buyers can receive a discount from about 3-12%.
Does anyone have any experience using this website? Using my Schwab credit card I can receive an additional 2% back on my purchase, which potentially gives you a few bucks back.
Do additional websites like this one exist out there?