My favorite method of exchanging has been in operation for some time with several traders. They send me stamps {used only) which are not in my MAIN LIST webpage, identified by Scott number. In exchange they get to pick stamps from this list, and I mail them back to them with a detailed statement listing the stamps traded, and showing the resulting catalogue value balance between us. Over a series of trades we manage to keep the balance close to zero. The only caveat is that I'm unable to accept certain countries at present, such as Israel, Germany DDR, South Africa, so it's best to check with me first.
Because my collection and duplicates are catalogued in a database (apart from a huge backlog waiting for a few spare months!), another way is that a collector sends me a list or spreadsheet listing their duplicates. We then request stamps from each others' lists, and work out a running balance by catalogue value, eventually equalizing the debits and credits.
If you prefer, I will give you three times the catalogue value in stamps of my choice (all different, none of them junk, and all cataloguing more than 25¢) in exchange for any of your stamps I keep.
On the other hand, you can select stamps you want from my lists, and "pay" for them with three times the value in postally used stamps of your choice, again provided they are not junk and all catalogue more than 25¢. Junk, in my view, is anything that most collectors don't like to receive. This includes many used recent definitives of major countries which appear to be overvalued by Scott, such as the Canadian $2 and $5 stamps. I will normally accept the stamps you send in "payment" but reserve the right to return any that I consider junk or flawed.
If you have surplus large quantities of the same stamp, so do I! To even out the overages and shortages, I find it useful to trade batches of 10 of a kind by any of the above methods. Click on the Wholesale button to see what I have to offer.
You can also purchase any of the stamps on my main list for one third of Scott catalogue value. I'm using the 2022 edition.