where will you take the spot price from?
The best price (highest) among Kraken, Bittrex, Poloniex, Bitstamp, Bitfinex, Exmo (and we are adding more markets) for the moment.
Looks a little suspicious. What do you gain from buying at a higher price?
Market price doesn't matter for me, because we give you cash by the rate we got during selling coins on the exchange market.
Easy: you send me 1 ETH, I sell my 1 ETH (to speed up deals we have depo on our markets' accounts to not wait until transaction will have necessary amount of confirmations) on the market for say 250 GBP. I have 250 GBP on my balance, I pay 250 GBP minus commission to you.
We earn our money from commission (and yes, while promoting our service on bitcointalk we earn nothing from buy deals).