Mass Effect & Mass Effect 2
The Migrant Fleet has little economic base, operating in a state of perpetual 'hand-to-mouth'. While quarian ships include light manufacturing and assembly plants, they lack heavy industries such as refining and shipbuilding. The fleet has tankers for water purification and oxygen cracking, but the space-intensive nature of agriculture limits food production. A single disaster could destroy the fragile balance.
The quarians earn income in creative ways. Because the government is obliged to provide food, water, air, and medical support for every individual, the Conclave strategically determines the course of the Fleet to bring in resources and income. A species who suspects the migrant fleet is headed towards their space often offers a 'gift' of surplus starships, fuel, and resources to convince the Conclave to alter course.
As the Fleet passes through a system, swarms of mining vessels work over asteroids for metals and siliceous materials and cometary bodies for water ice and organics. Quarian miners are adept at locating and strip-mining space-borne resources. This sparks conflict with corporations already working the system. Large mining concerns spend millions on lobbyists and public relations portraying the quarians as locusts, devouring the resources of a system before moving on.
The greatest asset of the quarians is their rarified skills. Most are experienced miners. Due to their life in perpetual salvage and repair, they are skill engineers and technicians. More than once, the very corporations that lobby against the quarians have made back room deals with the Fleet, arranging for skilled quarians to fill space engineering jobs that other species would demand higher wages for. Quarians are widely hated among the working classes. 'The quarians are coming to take our jobs' is a common response to the Fleet's approach.