EB Background check question

Had a weird time with most recent internship over last summer. Going to EB for SA in nyc this summer, and specifying this because I heard that BBs do harsher background checks? Anyway, was wondering if anyone could answer a few questions for few please and thanks! How do background checks at EB's work with 3rd party employees at hire right etc? Do they ask questions about previous internships or is it only to provide dates?  If they do want to contact a previous employer, do they ask you to provide a phone number, or do they just check for w-2 to confirm dates, or do they just call HR? (If they do call HR, what types of questions do they ask or is it just to solidify dates.)

Thank you again!