“However, most other suppliers still ask the customer to post their currency, so a trip to the Post Office is needed and this adds another expense to the process.
“There are high street vendors, such as Tesco, who still do some instore transactions, and of course the Post Office themselves.
“The major issue with these vendors, however, are the rates. These variations can be as much as 20 cents on the Euro from what you buy it from vendors for to the rate you sell it back to them at.”
One major red flag to look out for is if a currency seller tells you they are receiving zero percent commission.
source: express.co.uk