I bought, sold, traded and flipped powder burners for decades.
Just some lessons I learned over the years that may be applicable to air guns.
You can go broke buying good deals.
You cannot get all the good deals. There are plenty of others looking for deals.
Good deals are like city buses. if you missed the one you intended to catch, be patient. Another one will come along.
How do you define a good deal? Is it a great price on something you have had a long term desire to own? That is a good deal.
Is it a great price on something you never really wanted but recognize that it is priced lower than market value? not such a good deal. you now have something you never desired and the only attraction was that you got a good price before someone else did.
I try to keep all of this in mind when buying and selling. It helps to curb the frustration of missing a bargain.