Car repair shops say auto insurance companies are coercing them to use cheap parts and sometimes dangerous practices to fix vehicles involved in accidents. Headlights held together by glue, dented rims and a new hood that’s already coming apart are among the kinds of parts allegedly being pushed to go into cars as part of the repairs, according to some repair shops and attorneys general. Owners say the insurance companies steer their policy holders toward body shops that follow their rules, providing a vital source of business.