All items sold  clearly have an expected delivery date, does not matter what the seller says, once past that date the buyer can open a not received case to get a refund.

If seller does not refund then buyer escalates  to ebay who refund at seller’s expense and seller gets a defect.

Does not take many defects for seller to fall below standard, and get restrictions on selling.

It depends what they're selling, this is what defines a private seller/business seller. 300 items per year isn't a lot.

A private seller is one who is just selling off their own personal items such clothes from their wardrobe, bits from their loft/garage etc.

A Business seller is someone who buys or makes items to sell on, they may have multiples of the same item listed or brand new clothing/shoes in various different sizes.