I am looking a purchasing a used inflatable and the owner told me it needed to be topped off every couple of weeks. Is that normal?

Thanks!

the pontoons should hold air and not need topping up.

but

2 causes for topping up the pontoons

1] a slow leak. if it is just one section of the pontoon needs topping up, this is the problem

2] temperature changes. some boats have valves that will let out air [decrease the pressure] if the pontoons become over inflated. this is caused by "Charles's Law" [http://en.wikipedia.org/wiki/Charles's_law]. basically if its hot, the pontoons will be hard, high pressure. if it's cold, the pontoons will be soft, low pressure.

your man might be topping up the pontoons every couple of weeks when he sees it in the morning and thinks its low, its hard to tell via the internet.