There are 2 distinct tendencies in choosing your collaborator in the seo world: to use local companies (close to you area of activity in the "real world") and to use off-shore companies (the work over internet but they are located physical in other countries or continents).
Depending of your location, the local seo companies may be too expensive that you think the job it's worth paying for. They usually are - they measure the quality of their job and their needs and they tag some price to that, but that's another story. The good thing attached to that is that you have the same experiences and you often speak the same language (as you understand each other easier because you have the same background), they might know better how to meet your requirements for the site and the online with some kind of marketing in the real world in order to maximize the benefits the both sides of reality. Another good point is the time zone: it's the same with your's. No missed calls because they are sleeping when you need them the most.
One of the the greatest benefits of an off-shore seo company is the price, in times of a crises it's one of the most important element of criteria in selecting somebody. It may not be easy to meet them face to face, but the development of the online lately makes it easier to contact other people via phone calls and video calls - I know it does not compensate entirely the real discussion, but it has often good results. Always remember: when you work in the real physical world you have to target clients from your town, city and the nearby place; when you work online you can target the entire world. The seo is a very good extension for the real world marketing (there are fields of activity as online marketing but there are not very different of a good and efficient seo job). The geo location of search engine optimization and online marketing is very relevant for the success of you site, but that's a subject for another article. The point I want to make obvious is the an off-shore seo company can target the clients from a specific area of the Earth and it can even improve your own marketing (in your original location).
Not many people that does not work in the field realize that a software engineer/web designer & developer/seo expert (for example - the list can continue with a lot of other fields of activity) can work in any point of the globe where he/she have an internet connection, a working computer and some silence & good mood for what he/she does. The job done for you site is the same in Romania, Great Britain, USA, China or Japan no matter who does it. There are small differences from region to region, but usually they are about how the job is done not the results.
So, the most important thing (it can be a very good conclusion) you must do before choosing any king of seo company (local or off-shore) you must check their previous work and results. No matter their price, no matter what they know to do or their intention, be sure they can provide what you wand and what you need. Always ask for additional information if you are sure.
My recommendation is to check Supravirtual SRL, it's a small company in Oradea, Romania, Europe.