Hi David & Cheryl
Being a postcard dealer is not an exact science, and is a very long, facinating and frustrating learning curve. I learn something new every day - which is what makes it so much fun - nor are the prices you may find on ebay always an indication of the true value of a card (The Mark Twain thread is an excellent example of this)
- it very much depends on who is looking and when, where, what,condition, date and even to whom the card was sent in some cases.
I know how much I paid for each card I have, so anything over and above is a profit (taking into account fees, packaging time etc)I research as much as I can, and then I list and let the people of ebay make the final desision.
I sell worldwide as this gives me the widest possible audience.
After time you get a feel for the valuable cards, and having a variety of reference books, as well as web sites and ebay completed items helps with a starting price.
It is impossible to say which cards are "junk" and which are not, as there is no rhyme nor reason to why people buy the cards that they do. (I personally do not upset my cards by accusing them of being junk, and give them all a fighting chance!)
Fortunately for us die hard dealers that spend much of our time up to our eyes in books etc, it isn't a simple case of this card is worth X amount - as otherwise everybody would be doing it! Have fun, and enjoy the cards. Sometimes the suprises make the research worth every hour, and even if the card dosn't sell - think of the knowledge you have gained!
I hope I have been of some help, and wish you both well with your new ventures.