How can employers find out your employment history?

There is really no such thing as a employment history search. Employers generally use resume style information to verify employment. There is a database search they can conduct but not all employers report though many do. It would be important to know which ones may have reported to the database repositories. You can find a search of this nature here: http://www.efindoutthetruth.com/preemploymentscreening.htm

The only way an employer will know your employment history is if you tell them. Your previous employer obviously didn't verify the dates of employment. The background check and credit check is completely unrelated.

i work 4 h&r block and from exper. they may ask 4 a transcript for w-4purposes.however,you're their best source...

I own a recruiting firm in the New York City area and when we perform a background check, we check and confirm all dates of previous employment with past employers. If those dates don't match up with what is on the resume, it will raise a red flag and we begin to dig deeper. A lot of times, background checks continue even after you begin employment.