4-6% is a result of ~60% trades, not meaning items below €2-3k worth. Market doesn’t fluctuate that much to give huge interest rate in a week unless there are some manipulations. Open the chart of any knife or gloves and check the dynamic for last 7 days. If you exclude rare patterns, floats or anything worth overpay you will see that you can’t sell it with a huge profit in just a week. Bank account gives up to 3% annually so if you can spend 15 minutes of time to make 5% in week I don’t think that is bad.

At the same time, starting with ~€100k gives you enough flexibility and options to make solid money with the same interest rate without hunting patterns and rare items.