I was doing a similar thing (selling tax "included") and just avoiding mentioning the whole subject.
With the exchange rate deterioration and fee increases etc I could no longer afford to give this bonus to my (limited) Canadian buyers.
I now charge GST/HST to Canadians (I mention it in my TOS) and so far have had only 2 buyers question it (after they had purchased), naturally enough both buyers were from the land of the "taxless" (Alberta).
I don't think anyone reads the TOS so I doubt the fact that I mention it has much effect on buyers.
In most cases Canadian buyers have to pay these taxes when they buy from the USA (CP/Customs collects it) so they have no reason to bitch about it. The people who do are also the ones to complain about my shipping charges which in Canada are actual postage plus less than $1. These buyers will complain about anything!
Wrightcomputes....you're right about eBay, they haven't a clue but the same could be said for most programmers...they have NO real life experience which is why so much software works just fine in the "lab" but not in the real world.
I presume that ALL eBay.ca programming is done in the USA, when the day comes (and it will) when the US (state) authorities start cracking down on internet sales (tax) things will change. As you said the situation in the USA can be even more complex than Canada as in some states there are numerous different tax rates depending on the location of the seller and buyer.
Ben

"What else could I do? I had no trade so I became a peddler" - Lazarus Greenberg 1915

"What else could I do? I had no trade so I became a peddler" - Lazarus Greenberg 1915
- answering Trolls is voluntary, my policy is not to participate.