Is this a way for dodgy sellers to collect your details?
No, it isn't. Placing a bid doesn't give any of your details to the seller.
If an item disappears, it's either because the seller has withdrawn it from sale (for which eBay will penalise them, if bids have already been placed), or because eBay itself has removed the listing. This may be because it contravenes their listing policies in some way, or they have reason to believe that the listing may be fraudulent.
