Absolutely not!  Some online and desktop auction sniping services require you to share your eBay login information with them to place your bids.  We take advantage of eBay's linking service, just like PayPal and many other 3rd party eBay service providers.

When you add your eBay account to our service, we redirect you to eBay's website to log in to your account and grant us access to bidding.  eBay then adds a link between your eBay account and our service.  Finally, you have full transparency and control of the link within your eBay account.

You might have done something similar to this on Facebook or Google.  This allows us to snipe auctions and determine the outcome without you ever needing to disclose any login information.