Thanks to retailer influence on state legislatures, some states allow a retailer to bill an individual charged with shoplifting a specific amount set by law. The letters, usually from out of state lawyers, sound pretty intimidating. Although the letters may claim that the retailer may sue you if you do not pay the amount demanded, I have not ever seen or heard of anyone who ignores such a letter being sued. Some people hire lawyers to respond to the retailers. Lawyers then sometimes threaten the retailers with lawsuits themselves.
Although your case may well be different, people in your position have successfully ignored these letters. Ignoring these letters does not result in a criminal record. I suppose that the business could but something negative on your credit history, but so far, I have not ever seen that happen either.
This is a civil demand letter the only option Walmart has if you refuse to pay it is to file suit against you in small claims court. Since no police came out to the store it sounds like no one was charged with theft.
There are no criminal consequences for not paying the demand
Based on what you have written, it appears that no criminal charges for theft were filed against you or your sister. As for the letter you received from Walmart, are you sure that the letter came from Walmart or did it come from some lawfirm out of a different state saying that you had to pay $550.00? Assuming that the letter came from a out-of-state lawfirm; the letter was sent under chapter 134 of the Texas Civil Practice & Remedies Code (Texas Theft Liability Act). This form letter is generally an attempt to collect under a law which was created by the state legislature at the lobbying effects of retailers.
Generally, the retailers remedies for non payment of demand, is to take you to court and sue you in a civil proceeding in an attempt to obtain a civil judgment.
The above response given is not intended to create, nor does it create an on-going duty to respond to questions. Additionally, the response does not form an attorney-client relationship, nor is it intended to be anything other than an educated opinion. It should not be relied upon as legal advice. The response given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change.