I got a pop-up on Mercari offering $10 off my shipping and I just needed to add my payment option. Since it was through Mercari I thought it was trustful but then I got charged $2 without getting anything back. And then I was charged another $19 on my account. I was able to cancel easily since it was through PayPal, but when I called Free shipping.com for a refund they told me that I didn't have an account with them, even after I have them my info. Very shady business.