How do you choose an agency? It is better to contact marriage agencies that have been working for more than a year, or those that were established by people that had been working in another marriage agencies. An agency should at least have a computer with an Internet connection, a printer and a scanner. If the agency could arrange for visas both for the men who may want to visit you and for you if you decide to travel to an overseas fiancé, it is a good thing.
Try to find out, which foreign agencies they collaborate with, or whether they represent a particular foreign agency, whether they have results of their work - in other words, marriages. When you find several nice marriage agencies, choose the one that is situated not far from your home or office, or else it would be hard for you to find time to send or receive letters. The personality of the agency owner is also important - you would have to deal with this person quite frequently.
Do not give in to tricks like "We only get people together, and after that they stop needing our help, so we have no idea how many marriages were contracted as a result of our work". If people stop needing their help, it means something is wrong with them. Women usually do not share the details of their marriage quest with their friends, feeling embarrassed about doing it, so the only place to discuss the search process is the marriage agency. Moreover, if two people have found each other and are happy together, they usually do not forget to say "Thank you".
The main source of income for Russian marriage agencies is the fees men pay to correspond with the agency's female clients through the agency's email. If you want to get all the men's letters that are addressed to you, find out whether the agency requests payment for correspondence from men, and insist on getting all the letters that arrive for you, if you can afford to pay, of course (usually it is 10-25 rubles for a letter). If you have a "friendly" relationship with the agency staff, it would be easier.