Yes, obviously if selling you will need to add on the cost of sales tax, and if you paid to have the cases shipped to you, then you can make up for that in the cost, but it's best to itemize these when listing what you have for sale, so it is clear you are not trying to make a small profit. And I know when I shipped out catalogs, the envelopes needed were $0.50 a piece, cheapest I could get them, so I added that to the shipping cost, as it would have really added up otherwise. That's reasonable and I'm sure no one has a problem with that.
However, when trading, straight trades are probably best, one F?gure for one F?gure, regardless of how much you paid initially for it or what sales tax applied.
Paypal is the best and safest way, but keep in mind to account for the paypal fees and decide who pays those. I sometimes tend to forget about the fee. If you send the payment as a gift, you can choose to assume the fee yourself, and if paying directly from your bank account, there is no fee if sent as a gift.
