Legal Question in Personal Injury in Georgia

Sure, a seller can be sued and potentially liable, BUT you apparently were not. Unless and until you are, there is really nothing for you to do. You looked for the receipt and did not find it. Opinions might vary, but I would not contact a lawyer because they sent a letter merely asking you to contact them (IF that is all the letter said). If someone wants to contact you, they can pick up the phone instead of writing a letter asking you to contact them. If a lawyer contacts you and asks for the receipt again, you can tell them you looked and didn't find it. If they want to ask for more details, it is probably time to speak with a lawyer.

The number one manufacturer of propane tanks in the US is Worthington, so I assume that is the type of tank you are talking about. Worthington has national counsel out of San Francisco that defends claims aleging tank failures nation wide. There are propane tank failures, and lawsuits about those failures, all the time. You likely have liability insurance for your business. I think you need to report this contact to your insurance company and do what the insurance company says to do. If you get sued, and there is coverage for that lawsuit under your policy, the insurer will provide you with a lawyer at no charge to you and will defend (or settle, if need be) the claim. The primary defendant will be Worthington if there has been a failure of the tank due to negligent design. You will likely be let out of the case if the plaintiff were to sue you at all as there are several defenses you have to such a claim (i.e. you didn't do anything wrong just by selling the thing). But report the claim so nobody at the insurance company can say at a later time that you failed to report the claim timely which is something insurers sometimes raise to try to void coverage.

Yes you could possibly be liable (and you may also have defenses). There are lawsuits and claims of this type against at least one or more major tank companies. Generally the plaintiff's main target would be them. I am hoping you acted properly as to this from the initial complaint. As a business you obviously know to carry a very good high limit insurance policy, and they will defend you and pay claims as long as you give them notice. All you have to do is give them timely notice of this and do what they ask you to do (if you have not yet reported this, report it now). Note that if you don't make a timely report or answer his lawyer without their okay, they may decline to represent you and pay claims.