Hi emmabluewho, to expand on ninth's reply, you appear as a relative stranger to computer techie stuff so what you may not have realised is why your listings are actually on Auctiva and not on your PC. This is because you are creating your listings directly on Auctiva's machines and not yours.
You are using your PC as the tool via Internet Explorer and the internet to access Auctiva's listing editing tools on their machines. So when you save your listing from Auctiva's on-line editors then you are actually saving it at Auctiva.
They like any large computer based company will have significantly beter backup and data safety measures in place than individuals like us can afford to implement.
Their current and future $$$ depends on it.