There is usually a hydro test date that will eventually expire. If you have an expired tank, some places charge you the $10 recert fee, some dont.
Also depends on if where you get it filled swaps tanks or fills them. Its usually the places that fill them that charge the recert fee, the trade ins usually just go in a pile with other empty ones to go back to a filling station so they dont typically charge the recert fee at those places.