an investment company advertised that last year its clients on average made a profit of 10%

Answer 1

sounds similar to Bernie Madoff's investment claims, too good to be true, and it wasn't true

but is the 10% "profit" before or after inflation? If inflation is 10%, the real profit is zero. Which doesn't sound too good to be true, just misleading advertising. Still zero profit is better than negative profits

"on average" may also be misleading, as it might be skewed upwards due to a small number of clients who made much higher than average. The median profit may be more accurate, especially if the higher earners made their money off insider trading.