Payments on Marketplaces and Websites

[mani123]

What payment gateways do most BTC websites and marketplaces use? My main concern is to find out how does every transaction to and from a marketplace get mixed like the service of bitcoinfog, how is an escrow system built and how does on almost every BTC marketplace, the deposit address is always different?

FYI: I'm a web dev. who has 0 knowledge in project developments related to BTC and look forward to learn more.