I'm not sure what you mean by "other reputable vendors" - other than whom? Are there disreputable vendors out there? And I would imagine that sales tax is dependent on your country and/or state, but I have no idea what that is...
I have purchased my upgrades through regular software vendors such as pcconnection in the past. I know them and have found them to be reputable - meaning I can actually buy a real Adobe product - not a knockoff (knockoff vendors do sell Adobe products on the Internet). I can buy 11.5 full from pcconnection + no sales tax for 1078, but no upgrade - I need the upgrade. I can buy full from Amazon for 999 + no sales tax but no upgrade. I can even buy 11.0 at Amazon fro 265 + no sales tax but no upgrade. Is there anything in 11.5 worth buying - I don't see any, so maybe I should just buy 11.0?
One of the biggest advantages of buying online is that you normally do not have to pay sales taxes. Obviously I am not interested in wasting money. To buy the upgrade directly from Adobe costs 299.95 + 15 sales tax. I can buy an 11.5 license from Provantage for 284 + 3.95 licence processing fee, but who is Provantage - is this a real Adobe license - where do I get the software from? I believe I have some legitimate questions here - where to buy the upgrade for the best legitimate price (preferably no sales tax)?
Edit: CostCentral has license available under TLP transactional licensing program for 300.75. What is this? Is this a proper way to buy one license?