Dealers send tools returned under the 30-day return policy to Festool. In the US, they are not resold to customers with the exception of something like the reconditioned tool sale we had last year, which only happens every 3-4 years. The tools are used by Festool employees, in our training centers, and I believe may be sold to dealers as demo tools upon request.
In reality, we don't get a lot of tools returned. So, it's not an issue of having a stockpile of them.
Shane