I also had some friends who did this around 2012-2013. It was pretty easy, and they were making 25-30% margins on the bitcoins that they sold. Sounds great!

They ended up getting scammed a few times, and they realized that it was a fairly efficient market after all. So they got out.

For buyers it wasn't easy back then. Now, in Spain, you can turn cash into bitcoins very easily. There are bitcoin ATMs in a lot of cities where you can buy/sell bitcoins anonymously with a 1000 euros limit.

With a bank account or debit card it's even easier.