I suggest you enter "how to check if phone is blocked" in Google. You will find plenty of advice there.
Why is it that so many new members of eBay seem to want to start by buying or selling an expensive phone? Without understanding anything about the risks of buying and selling here.
At least you're looking at an established business seller with good feedback and sound detailed seller ratings. This is important, as eBay's money back guarantee only lasts for 30 days. After that, if anything goes wrong you're reliant on the seller. Regrettably, one of the most frequently asked questions here is what to do when sellers don't want to know about problems, and their warranties prove worthless (the answer is that eBay and Paypal won't get involved, and you're on your own). No doubt there are plenty of sellers who do honour their warranties, but we don't hear about these. It's up to you to make your own judgement - there are no certainties when buying on eBay.
Do you buy a new phone from a known retailer and the certainty of a full manufacturer's guarantee? Or buy a higher specified but pre-owned phone on eBay, and back your own judgement of the service you can expect from the seller? It's your call.
