If the items were produced as collectibles (like decorator plates or Franklin Mint products) the person who owns them is probably the last customer.
That is, the entire market was saturated by the company producing the "collectible" and there are no new collectors nor are there any collectors who did not buy when the items came out first.
In addition, you have to watch your demographics. The little girls who deeply desired a Shirley Temple doll are now in their 80s and disposing of collections. The girls who wanted a Barbara Ann Scott doll are in their 70s and bought one 15 years ago as a retirement present.
In other words, collectibles go out of fashion.
But they also come back into fashion. "Rocket Mail" was a big deal in the stamp collecting world in the 1930s then almost disappeared until the late 1990s, when there was a small but definite resurgence of interest.
Your friends should do a little buying to build up their feedback before listing a few low value but interesting items to test their skills.
Your input should be limited to helping with the rules, teaching how to write a good title, and setting up a Paypal account.
Don't get talked into selling for them if you value their friendship.