Like Kanga said. When I did mail-order, the old fashioned way, I would send my price lists using stamps that I bought at 70% of face, from stamp dealers, who would be making a profit at that rate..
I have thousands of the useless wallpaper. I group them for postage. Put all old Christmas stamps on Christmas cards. Used a bunch of bi-centennials for a post to an American Revolution Org. The USPS and the US Mint are going the same way - flood the market with useless garbage and hope the suckers will buy it. I got out of USPS collecting in 2001 and am out of the US Mint scams now.
When I was going to local shows in person, there were usually at least one or two stamp dealers there selling common old postage for well under face value. I decided that now that I can print postage, it's not worth my time to try to save money that way. It is fun to see the old stamps, though.
I routinely use old unused postage stamps for first class mail. Try to keep the number of stamps down to three commemoratives or four small size. Unfortunately I got stuck with a lot of six and eight stamps that I bought in the 60s and 70s. But the old Liberty Series stamps dress up envelopes nicely.
My wife's organization sends cards and gifts to ladies who serve in the armed forces overseas. I always put old patriotic stamps on them.
I saw an ad in a gun magazine by an old dealer in parts. He wrote that if you wanted a list just send him a SASE. I wonder how many readers picked up on that.
Daughters of the American Revolution. My wife is a member. I am a member of the Sons of the American Revolution. My wife also has direct links to the Mayflower and is in some of their groups.
Remember those round dishes with the wet sponge? Automatic stamp licking - just swipe the stamp across it, and viola!
What fun! I like to keep an eye out for those Mystic or Kenmore deals where you get 50 stamps for $1 or whatever. I've gotten well over the price paid in FV of old stamps, which I then use to send coins and letters in the mail. Since these stamps are worth so little on the secondary market, I may as well use them in commerce.
These a couple i saved... the canadian one surprised me had tracking and all didn't expect $15 in stamps on it lol and the other well not often i get russian stamps
If you want to see just how badly stamps have depreciated in recent decades, here's a great example I received in 2019.