Depending on where they are coming from, you might need to consider a number of things. Most overseas adoptions are facilitated by rescues with premises in the UK, so they will manage the practicalities of importation and paperwork.
Depending on where the dog has been, you may need to consider what diseases and parasites they have been exposed to (and if they have ongoing issues with say, Leish). Some of these diseases and parasites are rare or not present in the UK, so your vet might not be looking for them unless you give them the dog's background.
Also bear in mind that if a dog has been chipped overseas the chip may well have been implanted in a different part of the body which will often lead to confusion when they are scanned here. Many dogs in mainland Europe are chipped in the neck area rather than between the shoulders as is customary in the UK.
Really, so much depends on what country they are coming from and what condition they are in. Taking on a dog that has had severe health issues and/or very poor treatment is not always easy, and your heart should be ruled by your head, unless you are experienced and willing to work with some of the issues.
Finally there is also the issue that there is no shortage of dogs needing homes in the UK, and it may well be more sustainable to donate to an overseas shelter to assist in vet care, neutering programmes etc rather than just spending a lot of money on importing small numbers of dogs. For instance the £1000 quoted upthread could have been spent more fruitfully in a spaying programme - that could probably have benefited a dozen bitches.