They type of shops became increasingly a staple of larger cities in the Eastern bloc from the late Thaw onwards. These well-lit and stocked differed markedly from the typical shopping centers for the Soviet and Eastern bloc public. this was because they were initially for the increasing numbers of Western and other non-Soviet tourists that visited beyond the Iron Curtain. The goal of the shops was two-fold. Firstly, even though the Thaw and Detente periods were both much more open than the Stalinist period, the authorities still liked to keep tight tabs on foreign visitors. These shops, such as the GDR's Intershop or the Soviet Beryozki, were ways to quarantine these foreign tourists and showcase the plenty of the planned economy, hence the Soviet-made goods which were often of higher quality than the items that could be purchased in the shops for the mass public. Secondly, and probably more importantly, these shops were the source of hard Western currency for regimes that were increasingly cash-strapped. The shops' Western goods, acquired through trade missions, were often a means of social lubricant for Western visitors within the Eastern bloc. In the institutionalized dearth of the planned economy, possession of high-quality Western goods allowed these foreigners to navigate the often strange waters they found in which they themselves. For example, Alon Nothnagle's blog posts on life in the GDR as a graduate student showcase how West German coffee was a much treasured luxury among his circle of East German friends. The Eastern bloc goods, especially alcohol, were often quite inexpensive by Western standards and thus also offered the visitors a cheap deal.

Although these shops were initially for Westerners and the Eastern bloc elite, by the late 1970s they had increasingly become more open to the broader public. It still was not an open-access market, some beryozka had guards or misleading signs, but the clientele for these shops gradually shifted from Western to Eastern customers. This was in no small part due to their use by the state as a safety valve for a general public that was unsatisfied with the planned economy. Allowing greater access to these stores and their Western goods would take the wind out of the sails of the black market in Western products and restore some faith in the Communist state by rewarding greater numbers of its population. In the GDR, currency reforms allowed for a greater number of shoppers as the Intershops no longer required Western currency. The result was that many of these shops introduced or replicated Western patterns of consumerism. One East German joke signifies the transformation of the Intershop into an enclave of Western capitalism in the 1980s: have you heard the news, someone has jumped over the counter of an Intershop and asked for asylum. The Western consumer goods from these shops became totems for a higher standard of living. In the end, these shops were an albatross around the Eastern bloc's collective necks during the 1980s as they were a persistent reminder that the much-trumpeted planned economy had failed to catch up with the West and both the Soviets and the Warsaw Pact states discovered they could not put the genie back in the bottle once they opened up these shops to their citizens.

Sources

Chernyshova, Natalya. Soviet Consumer Culture in the Brezhnev Era. New York: Routledge, 2013.

Eaton, Katherine Bliss. Daily Life in the Soviet Union. Westport, Conn: Greenwood Press, 2004.

Zatlin, Jonathan R. The Currency of Socialism: Money and Political Culture in East Germany. Washington, D.C.: German Historical Institute, 2007.

In Poland, both local goods as well as imported goods were sold. Those shops catered to foreigners, as well as locals returning from foreign jobs. From 1975 on the system got so cynical that commies stopped pretending it was for tourists only, and opened them for everyone.

The point was to get as much real ("hard") currency as possible. Example: they sold vodka for 80 US cents (1988 value) per 0.5l, or Wrangler jeans for $11-13 (1988 value). (Source #1)

Other items sold were locally-produced home appliances and cars. The reason again was to get the hard currency from the population to the state. Those goods were hardly available in 1980's, simply not in shops, so one can think of those hard currency stores as "business class", for the privileged.

Just as there were two "sales channels", there were two exchange rates, the official, and the black market rate. Neither was actually any close to real marked value, the official was a rip off, and the black market value was bloated to about 300% (see source #2)

This source gives the inflation rate of US dollar (USD) between 1988 and 2015 at 99.6%, so roughly double the price. Vodka for $1.60 was the reason why Polish ferries to Sweden were so popular, but I have no reliable sources to answer why the jeans were do cheap. I personally think it was because of relatively low sales cost, hence much smaller margin.

Sources: #1 Pewex catalogue 1988 #2 www.nbp.pl, Polish National Bank, exchange rates for USD and DEM between mid-1989 and end 1989 show a 2/3 drop in the ex. rate