Perhaps not AV, but some airlines are smart enough to deflect this tactic, however, so it doesn't always work. United, for example, will base the point of sale based on the billing address of the credit card you use. Even if you, say, start out on their UK site to price out in GBP, when you check out, if you change the credit card billing country, to say, the U.S. when you try to pay, it will not only just change to US currency, but also price based on the U.S. point of sale. Many EU and Asian carriers automatically redirect you to the local site of the country where you are departing from - based on your search. For example, I tried to buy a ticket on BA from LHR - MAD a while ago, and wanted to pay in USD since that's where I live. Once you select LHR as the departure airport, however, everything changes to GBP and puts you to their UK site. Ditto with LH, TK, TG, CX and SQ that I've personally experienced. I'm sure there's more.

That's not to say you can't use a local online travel agency. Though some of them restrict the use of international credit cards, so again, can stop foreigners from buying at the local prices.