It’s fine as long as you’re smart about it. Try to buy local, if you can. This allows you and the seller to meet at a neutral location like a police station, where you can ensure a safe transaction for everyone, and you can actually ask to see it powered on and make sure it works.

If you have to buy used to be shipped, just ask for pictures and videos to verify the condition and see it working. If something does go wrong, these can be used to support yourself in a claim against the seller. When purchasing online always use a credit card that includes buyer protection or something like PayPal, where there’s a defined dispute process. Never use a bank account or debit card, as these are treated as cash and it’s nearly impossible to get your money back if the seller tries to scam you.