To relist I believe you will have to create another listing, unless you used Turbo Lister.
You can only view items from your feedback score, but only from the last 3 months, beyond that you can see who you have bought from and look at there current sale items.
Sniping is bidding in the last few seconds to try to stop anyone from out bidding you, but be aware your highest bid can still be below any automatic bid in place, there is also software/website to create a sniping bid for you.