I think we can reasonably say that the avast detection was good.
Absolutely. 
I thank you all for your able (and fast!) replies. I've been wanting to order something thru this eShop for a while, but keep running into this problem. And the owner, while 'Net savvy, is not a programmer, and has said a couple of times that the site is okay now.
So I really needed an external reality check to find out if I had a mis-configured browser cache, or something. This eShop is hosted with a provider that I also use; and I need to be thoroughly convinced that there's no/little chance of cross-contamination before I take MY eShop live.
Again, thank you all so much. I apologize for posting this in the wrong forum.