If your credit score was at the mercy of everyone who tried to lure you into accepting a credit offer, that wouldn't be fair -- after all, you have no control over their actions. Lenders routinely check the credit reports of those they might want to extend credit to, but these are "soft" inquiries. They don't count and they can't hurt your credit score.
Hard vs. Soft Inquiries
When you personally initiate a review of your credit report, this creates a hard inquiry. This would occur if you apply for a loan, a credit card or a mortgage and authorize the lender to look into your borrowing history. It all comes down to who prompted the check -- you or someone unbeknownst to you, such as lenders who dangle the carrot of a preapproved loan. Inquiries from potential employers also are soft checks, even if you prompted the inquiry by applying for a job. You didn't apply for credit, so they don't count.
Effect on Your Credit
Soft credit checks have no effect on your credit score and no one but you can see them on your report. In contrast, hard inquiries appear on your report for two years, although they only count against your score for a year. Too many hard inquiries can ding your score, but won't hurt it as much as a 30-day delinquency does.