Anything that is found on private property is okay to sell. So long as you sell them with a letter of provenience and specifically stating the date you found them is okay. date is very important. You might have a hard time selling them However, if you do have a buyer it's important for you to clearly tell them where they were found. If they still want them they are assuming the risk at that point.
Bsit...I dont think they were trying to sell things, but had a question about selling. It's probably a viable question that people might be interested in?
Hippy