Qatari Government can easily get rid of the troubles these agents are causing. The idea is to start a database and a housing authority (dont know if there is already one)

All the expatriates who have a family visa should register their house numbers / I.D. Card numbers with the housing authority. The housing authority's job should be to make sure that a person on family visa should only be able to register one house under his name and they should make it compulsory for ever expatriate to register his house number.
In this case an Agent would not be able to register more than one house on his name. Moreover the bachelors should be made to live in accomodation for Bachelors. and they should not be allowed to rent villas and other accomodations suitable for the families. This would definitely ease the housing crisis going on in Qatar. This idea was floated long time ago but it did not get the Government's approval. Guess government does not want to help the expatriates as the housing crisis is directly favoring the Qataris. (Who knows)