[mothered]

I got a dyson fan for £499 on eBay official dyson outlet

Is It the actual Dyson eBay store?

it arrived to my sisters address and she answered the door but didn’t sign for it

Was the package purely handed over to your sister without any form of verification?

she wasn’t sure if they took a picture

What events took place from when she accepted the package, to when the driver left?

I checked my emails and the tracking and it just says it was delivered to the address and then my sisters name on it

Email messages are not always a representation of the carrier's records on their Internal systems.

What options do I have here?

It depends on your responses to the above questions.