If I download books with a free trial, what happens if I cancel?

I always see audiobooks listed for free with a free trial... its not my ideal format but I'd choose that over a hardback any day, in the event that paperback isn't available.

What would happen if I dont subscribe to Audible? do I still have access to the books?

Also, does it only work on a subscription basis? or can I just purchase audiobooks as a one-off?