The spikes are predictable
New year and late spring. Budget planned on December data is wrong twice a year. Ramp before the curve so the bidding learns at the higher level in advance.
Freight is the hidden cost
Heavy items carry shipping costs that can exceed the ad cost. Break-even has to be calculated on landed cost or you will scale confidently into a loss.
Claims put you near the line
Performance and health benefits are restricted territory. The equipment is usually fine; the promise around it is what gets flagged.
More: the fitness niche page.