A Best Offer more than the Starting Price of an auction is to be expected (as opposed to more than a Buy It Now price which is a huge red flag). But, you are a new seller. You are going to attract more scammers than legitimate buyers. To keep the scammers from committing to buy your item (and tying it while you go through the unpaid item process) don't use auctions or Best Offer. List as fixed-price Buy It Now only and set the BIN to Immediate Payment Required. Click "Payments managed by eBay" in the "Preferences" section of the "Complete your listing" page of the new listing flow and check the box for "Require immediate payment when buyer uses Buy It Now" at the top of resulting popup.
eBay is experimenting with requiring pre-authorization for payment when a buyer makes a Best Offer but that's just an experiment and not applicable to all buyers (as a seller you can opt out--it makes combined shipping discounts difficult to impossible--or into the experiment in your Buyer Requirements). Otherwise auctions and Best Offer (and some Buy It Now) allow the buyer to promise to pay in order to scam you.
Note that anyone requesting you to contact them outside the eBay message system (email or text or phone) is almost certainly a scammer trying to get your contact information (e.g. to send you a fake payment message). Any mention of a gift card is also a red flag (they make the real money getting sellers to buy gift cards to send with the package for which they "pay" extra in the fake payment message).
Respond to any message wanting you to text or email or call that you only communicate via eBay messaging, and cancel for non-payment after the 4 days is up if s/he has already committed to buy. Make sure your Buyer Requirements are set up to block anyone with 2 or more unpaid cancellations in the past 12 months and those with primary shipping addresses in locations you don't ship to (and opt in or out of the pre-authorization experiment as your situation warrants). Add anyone who doesn't pay to your Blocked Bidder/Buyer List (and anyone wanting you to contact him/her outside the messaging system). But the scammers can create new accounts a lot faster than eBay can remove the ones that prove to be scammers. And some have the skills to hijack established accounts to scam with, so don't think it's only new accounts that can get you. Be wary of anyone requesting anything out of the normal flow of eBay business (you list, possibly they ask legitimate questions solely with the messaging system, someone uses the buttons you choose to buy/win the item, they pay, you ship to the address given with the payment, eBay tells you on the website--don't rely on email or text messages and don't click any links in them--that the funds have cleared and it's OK to ship).
