"Worst of the worst" is not an interpretation
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The Worst of the Worst Used Cars
"These 2006-15 models have a record of below-average overall reliability. ... they’re models with much-worse-than-average overall reliability based on multiple years of data. We recommend skipping all of them"
CHEVROLET
Avalanche, Camaro, Cobalt, Colorado, Corvette, Cruze, Equinox, HHR, Impala, Malibu, Silverado, Sonic, Suburban, Tahoe, TrailBlazer, Traverse, Uplander
BUICK
Enclave, LaCrosse, Lucerne, Rainer, Regal, Rendezvous, Terraza
GMC
Acadia, Canyon, Envoy, Sierra, Terrain	, Yukon, Yukon XL
CADILLAC
ATS, CTS, DTS, Escalade, SRX, XTS
PONTIAC
G5, Montana SV6
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http://www.consumerreports.org/used-car-buying/used-cars-to-avoid-buying/