I used my credit card last month, when the bill arrives I’ll pay it off. If you pay interest to the bank that’s money you can’t spend on those little luxuries that make life more bearable. Paying extra for goods so you can get ‘interest free’ credit is the same or paying extra for monthly instalments.
I started lending money to other people through Zopa, a couple of years ago. I get higher interest rates if I lend to people who are considered riskier. The A* market is the safest and I have no bad payers in that market or the A market. I have half a dozen late payers in the B market.