You found something online you must have.
But the retailer, even with a secure site ('https' in the URL at the point where you put in your credit card, plus a solid padlock icon in the lower-right hand corner of your browser) -- is a virtual unknown.
You may have the option of getting a TEMPORARY CREDIT CARD NUMBER from your credit card issuer.
Ask your credit card company to give you a temporary number for a single transaction. The transaction is still billed to your regular account, but the difference is your regular number is blocked. The retailer never sees or possesses your regular number. All it sees is the temporary number. Perfect for a one-time purchase!