Anyone can hold collateral. It doesn't require any special equipment. It's ridiculously good pay for the time, usually, but in cases where there's a dispute and a weak contract, it can easily take up way more time than it's worth, especially when there's a language barrier.

Actually - I forgot to mention something pretty important - multi-sig escrow, where you don't even have to worry about the escrow agent running off with the money (unless either the buyer or seller are colluding with the escrow agent to scam one of the other guys). Forbes has an article on multi-sig and some of the implications here: http://www.forbes.com/sites/johnvillasenor/2014/03/28/could-multisig-help-bring-consumer-protection-to-bitcoin-transactions/