That has scam written all over it, either they are going to turn up and pretend to pay with a fake app on the phone then claim there is some sort of delay or they will use a hacked account to send the money, the only way you can be safe is if you ask to see government photo ID and the bank card the bt payment is coming from, take pictures of them, and don't under any circumstances let's the bike go untill you see the money in your account, it's always handy to ask them to send £1. In advance they the remainder will clear quicker, but the I'd and bank card advice still applies, also the I'm going to send a friend thing has red flags all over it...