I bought some items from ebay that I can’t get to work, seller says he tested them but none the less they don’t work for me. I asked for a refund he said ok return them and I will refund you. My question is what is the obligation on him to refund.

i) just the purchase cost
ii) initial postage cost to me
iii) return postage cost

is it just i) and if he only does i) will eBay care about ii and iii) if I try and raise a complaint?

It’s not a massive sum so may be best just to write it off to experience!

Raise the return through eBay. They should give you a postage label so is there is no further cost. You should then get a full refund for purchase and original postage.

If you paid with/through PayPal they will refund your return costs. Google PayPal free returns..

As above, just raise the dispute not as described and that you want to return them and eBay will message you a returns label