I guess the number one thing to remember is always use a trusted & secure site. You should definitely call your credit card company immediately if you suspect fraud, they’;re actually pretty good at reversing charges.
I think this is looks terrible in the interface, the way WhatsApp uses the v or vv is much cleaner. And please don';t call it a "read receipts" it';s more like a "has opened receipt" does not at all tell if the receiving end read it! This is broken, old technology that should be replaced by something better!