Just avoid these cars with "worst of the worst" reliability:
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List of Used Cars to Avoid Buying by Consumer reports
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"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" 
The Worst of the Worst Used Cars 
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/