Let's follow up on the hacking issue.
Real world, that is a valuable skill set. Governments use substantial resources to keep information secure, and to compromise information held by other governments. Organizations do the same, although to a lesser extent.
But the Quarians have those skills, seemingly in abundance. Since they seem to be despised, they probably couldn't get government jobs - but they would be perfect for those who wanted that information. And, because their reptuation is already bad, the downside would be minimum.
Speculation: the Shadow Broker, and perhaps a variety of others, use Quarian expertise to compromise computer networks around the galaxy and on the extranet. They get revenue or other resources in payment. This would tend to keep them unpopular over time.
On the other issue of cottage industries, consider Iceland. Small country, problems with import/export, poor after the bank failure. Unpopular after the Icesave debacle. They sell some of their specialties - woolens, for example. I would think the Quarians would have some specialized things they could sell in the galactic market. Keep in mind, their labor costs would be minimal...