Selling on Ebay sucks. If you want to receive payment fast you have to use Paypal. They set all the rules and the seller is at the whim of Ebay, Paypal and the buyer all three of which can potentially screw you over. Right now I have over a 100$ being kept by Paypal for 21 days, a standard ebay policy if you haven't sold a ton of stuff yet and the item you're selling is over 100$. That is despite having a 100% squeaky clean record with both Paypal and Ebay. Selling stuff for emergency cash is not advisable unless you do a cash payment with local pickup.

In the UK we have Gocardless which would be ideal for receiving payments, except there isn't a marketplace I know that supports it.