Buying Old Time Radio mp3 cds via Ebay can be quite a challenge.  To not get "burned" (as I've been) follow these tips.
    1 - Look for items that list what the cd holds.  A buyer might say that his cd has 500 episodes but some of them could be duplicates.  Buying from a certain buyer because he lists the most episodes might be a mistake.  Some old time radio shows have different titles for the same episodes which can be misleading.  If you're not sure of episode titles, a great source to check is Jerry Haendiges' Vintage Radio Site located at http://www.otrsite.com/radiolog/.  It is a very accurate, comprehensive site.
    2 - Watch for listing that promise full episodes.  I've purchased cds from certain dealers because they've listed that they have a specific episode, yet when I listen to the episode, it ends abruptly in the middle.  Talk about frustrating!  Some shows only have half episodes available because the full episode no longer exists.   Reputable dealers will either not sell partial episodes or will let you know what you're getting before they sell to you.
    3 - Buy from someone with a decent feedback rating.  Before you purchase, read what other buyers have said about your seller.  If there's a common problem with their cds it will probably be mentioned in the feedback.
    4 - If you'd like to know the order of the episodes on your cd, look for a seller that labels his cds with the show titles.  When there are hundreds of episodes on a cd, it's nice to be able to find a specific episode.
    5 - Finally, watch shipping charges.  It costs less than $1 for a seller to ship one cd via first class mail in the USA.  If someone is charging more than that, the charges are going for something other than shipping (probably a large "handling" fee).