There's also sellers who are just starting out on Ebay, if no-one ever gave them a chance they'd always have no feedback, but buying from them is a pure gamble unless you can get information about them elsewhere and there's also the chance they could be using a dupe account because of previous low feedback scores, this maybe against Ebay's terms, but it won't stop some people from doing it and they could easily just use another name to sign up with, E.g. another family member, friend or colleague. It's a personal preference whether to give them a chance or not, if I was to consider it I would look for a phone number for the seller if one was available and/or I'd see if they have a website with reputation elsewhere. I'd probably get my friend to call them to ask them about the product and see how reasonable they sound, because I'm not the best at using the phone to call strangers or to make a judgement on the person.
If a seller has sold a reasonable amount of items and they've got less than a 100% feedback, then as long as they've got over 95% I will look at the actual feedback itself to see why they haven't got 100% and if I'm buying a particular item that I'm not 100% familiar with I will especially look for feedback against that exact item if there is any, I will also look for the same item elsewhere on Ebay along with feedback scores as well as reviews on other sites if they're available, if not I'd be more reluctant because there's a fair amount of low quality unbranded items selling on Ebay. If the item is used then the sellers feedback is even more important because you're trusting them to give you an accurate description about the condition Etc. and used items don't come with the same warranty. Sometimes negative feedback isn't always the seller's fault or you can understand why, E.g. they could get negative feedback just because the item wasn't what a person personally wanted despite the description being good, even if they gave a full refund without any issues, or there maybe negative feedback for the very occasional faulty item, but if the seller replaced or refunded without any quibble I wouldn't be too concerned as long as it is only occasionally because this can happen to any seller. Also if a company sells many thousands of items they're bound to get the very occasional negative feedback and a very small percentage of buyers aren't reasonable and they might give negative feedback in unfair situations, so I also wouldn't be too concerned if their feedback score is 98% or more as long as the bad feedback isn't something that shows consistent bad customer service or it's mostly related to the particular item that you're considering buying.
Watch out for very inferior cheap and illegal counterfeit items because from experience Ebay really don't care even if you report receiving one. My friend received a counterfeit "Sony" memory card for his camcorder once that was abysmal and kept giving errors, it didn't have a proper hologram like the genuine one and the camcorder itself even warned that it wasn't a genuine Sony memory card every single time he attempted to use it, but Ebay still refused to ban the seller from continuing his illegal business and he continued selling them along with other dodgy memory cards, instead Ebay only told the seller to refund for the specific item despite my friend's protests after showing them hard evidence of his illegal activity, they even told my friend to return the illegal item to the dodgy seller so he could sell it on Ebay again and of course so my friend no longer had the evidence, this was utterly shocking and just goes to show how totally incompetent Ebay truly are. In fact Ebay staff were now aiding and abetting a criminal, so don't expect Ebay customer service to be any good if something does go wrong and the payment processor Paypal most definitely can't be trusted either, in fact they're so bad it's best not to use them, but if you have to never keep a significant balance, please
click here if you wish to know why and read some of the shocking complaints, this is more significant if you wished to become a seller and even more so if you were in business.
I personally only deal with sellers from my country (in my case the UK) because it's easier to deal with if something goes wrong and the shipping times are much shorter, but watch out for sellers that have a local proxy postal address, but are really from other countries such as China, you can often tell by the long shipping time. Chinese sellers that offer free P&P are very common because the Chinese government is currently paying the cheapest postage costs for exported items as a perk to encourage international trade, I'm sure that many Chinese sellers are reputable, but I personally prefer to deal more locally and I don't trust any seller that tries to deceive people of their country of origin.
If I was selling then I would again look into the person's feedback in more detail and I wouldn't sell to anyone with any less than 95%. Again if they don't have a feedback score it's a pure gamble and there's unlikely to be any information about them elsewhere, so it's a personal preference whether to give them a chance of not. I suppose you could ask them to call you if you were comfortable in giving them your phone number to see how they sound over the phone if they decide to call, or better you could give them a mobile number you're not too bothered about sharing.