Most unreliable shops share observable traits that can be checked before any money changes hands. Domain age, archive history, and the presence or absence of independent reviews are the three fastest signals, and all three are free to check with public tools.
No single check is conclusive. A new domain may belong to a genuine new business, and an old domain may have been abandoned or compromised. The reliable approach is cumulative: several weak signals together justify walking away, and a payment method with dispute protection is the final safety net when doubt remains.