To be fair, English is not the most used language in the world. Only 5.43% of the world can speak English, compared to Chinese Mandarin (14.4%) and Spanish (6.15%)

http://en.wikipedia.org/wiki/List_of...ative_speakers

So it could very well be likely that the merchant could actually not speak English, especially if said merchant is in a non-touristy part of Spain where they are less likely to see English speaking tourists.

At least Spain would be a cinch for many Americans as many have taken Spanish as their second foreign language requirement in high school (I would've chosen Chinese but it wasn't offered at my school ). "No dolares, en euro por favor!"