Is it cheaper to buy flights from abroad?

But I got to wondering, is it ever cheaper to buy tickets online from another country (possibly in a different currency)? The online flight sites often geolocate you but there are plenty of free VPNs.

If you are talking about buying exactly the same ticket but purchasing from an alternative sales location, then yes, the price can be different. This is because—

1. the “availability” of a flight (how full it appears to a sales agent) can be varied by sales office,
2. the fare tariff itself may be varied by office, and
3. certain fares may be unavailable to purchase within certain countries.

For internet sales, the sales office location can be decided based on the airport of departure, or the internet domain visited.

For instance, Expedia will choose a sales office based on which of their domains you visit; expedia.fr may show a different price to expedia.ar, for exactly the same itinerary.

Most airlines will pick the sales office to be the same location as your airport of departure. In this case, if you buy a ticket starting in London, you will be given a London price, even if you visited the Japanese website. Indeed, you will usually be redirected to the UK version of the airline’s website.

This is illegal, but not uncommon, within the European Common Aviation Area.

In principle, however, this activity is illegal for carriers selling tickets departing from the European Common Aviation Area (which includes all of the EU, Switzerland, Iceland, Norway, and a few other states) by virtue of EC Regulation 1008/2008, Article 23(2):

2. (…) access to air fares and air rates for air services from an airport located in the territory of a Member State to which the Treaty applies, available to the general public shall be granted without any discrimination based on the nationality or the place of residence of the customer or on the place of establishment of the air carrier’s agent or other ticket seller within the Community.

[The Regulation is incorporated into the law of the non-EU states by the European Common Aviation Area treaty.]

However, certain air carriers do act in violation of this law; Lufthansa, Air France, and British Airways I have seen set prices slightly differently for different sales offices within the EU. I have seen Qatar set prices completely differently. Sometimes this can be remedied by calling and asking for the sale to be made from a different office (assuming you have already researched the price at different offices).

Within South America, it is common to have a different price for in-country sales.

This does seem a bit antiquated: LATAM publishes different fares for sale within Chile than outside Chile. (This different to a residents’ only fare, which is a different matter.) These days it is trivial to go to lan.cl instead of lan.com and buy the lower fare—if you know where to look, of course.

You will see the sales restriction in Category 15 of the fare rules, if you wish to inspect them; for instance, the SCL-IPC (Santiago to Easter Island) ILEEV244 fare contains the restriction

SALES RESTRICTIONS
    TICKETS MAY ONLY BE SOLD IN CHILE.

Whereas the much more expensive ILEEV967 fare says

SALES RESTRICTIONS
    TICKETS MAY ONLY BE SOLD IN EUROPE.

Note that if you choose to buy from lan.cl, your contract is considered formed in Chile and subject to Chilean law.

You can investigate using ITA Matrix.

The advanced options for ITA Matrix includes the ability to set the Sales City: you can use this to compare the effect of buying the same itinerary from different offices.

Yes, prices depend on the country you buy them from.

Prices are usually really different for pairs of countries with different standards of living. This is one of the pricing techniques to get more revenue (setting the prices based on what people are eager to pay, not on the cost) and the underlying idea is that you can market a flight for a more expensive price in a richer country. It may also depend on the currency conversion rate. So in your case (UK-Europe), the difference a priori is not significant, if there is one at all.

This is usually implemented with techniques preventing the customers to book from another country. IP filters may be used, as well as language constraints, and simply you may have to book a round-trip from the origin country (and one-way are priced significantly higher).

From the UK to “Europe” is a pretty broad category.

Discounts will more be a function of which country and which carrier it is, rather than where the tickets were purchased.

In many cases countries subsidize their national airline and simultaneously tax foreign carriers. For this reason using the “local” airline can sometimes be cheaper than using a foreign carrier, especially if the destination is a small, tourism-oriented country.

You will find that you tend to get the UK prices when your travel starts and ends in the UK.
You can buy two individual one way tickets without showing that you are from the UK.

I have booked tickets to and from the UK (starting from the Netherlands) and got the same kind of prices as my UK friends got for traveling to the Netherlands, so I am not sure that your difference in price is as general as you assume it is.