I had a Maverick 88 from the early 1990s with a single action bar, as was the case with older Mossberg 500s. Newer models of both have dual bars.
In 1988 Mossberg opened a plant in Torreon, Mexico, to make parts, which are then assembled across the border at the company's Eagle Pass, Texas, facility. I seem to recall the reason, at the time at least, was Mexico's restriction on the manufacture of firearms. Component parts, however, can be made, and with the cheaper labor costs south of the border, the Torreon plant is probably seeing more and more of Mossberg's production.
Mossberg has been marketing less expensive shotguns under the Maverick Arms name since 1989, shortly after the Torreon plant opened. The Maverick 88 uses the same stocks, barrels and some internal parts as the Mossberg 500, but as others have pointed out, uses a trigger guard mounted safety rather than a receiver mounted version like the 500.
An indication of how similar the two series may be is that Mossberg currently lists the Eagle Pass address for service on both the Model 500 and Maverick line.