Ask for a certificate of insurance sent directly from their carrier, check that the business entity and address are real, call two references from jobs over a year old, and be wary of large deposits and same-day pricing.
More detail
Texas does not license general contractors at the state level the way it licenses electricians and plumbers, so a general contractor cannot show you a state contractor license because there is not one to show. That makes the other checks matter more, not less. What to verify, in order. A certificate of insurance for general liability and workers compensation, sent to you directly by the insurance agent rather than handed over as a PDF, because certificates are easy to alter and easy to let lapse. The business entity registered with the Texas Secretary of State, matching the name on the contract. A physical address that is not only a PO box. And the trade licenses for the licensed portions of the work: electrical, plumbing, and HVAC are state-licensed in Texas and those numbers are verifiable. References worth calling are the ones from a year or more ago, not last month. Recent customers are still in the honeymoon; the ones from two winters back know whether the callbacks got answered. Ask specifically whether the final price matched the contract and how change orders were handled. Deposit norms. A deposit is normal, and a large one is not. Material deposits for special-order items are reasonable and should be documented against the actual order. A request for a third or half of the job before anything is delivered is a working capital problem, and you are the one funding it. The pressure signals that correlate with trouble: a price that expires today, a discount for signing now, a contract that is a one-page estimate with no scope, and a request to pay in cash. None of these are proof of anything on their own, and together they are a pattern.