Cheapskate: Someone looking to make a bargain-combine postage, lessen postage, etc.
Delboy French: Trying to communicate with other Ebays in their own language, or the stuff you put on envelopes to France, etc.
Fiddlers: The customs people, especially if they open an item to look inside.
Gazump: To bid at the last moment, especially if it seems by artificial means.
Granny's Attic: A seller selling old nicknacks.
Nightowl: A seller whose items finish in the wee small hours.
Overkiller: Someone who lists the same item too many times.
Quizzer: Someone who asks a question you can't answer.
Rule of Second Chance: The only items that you will be able to give a second chance offer to will be ones that you only bought one of.
Rulebook: Someone who always fills their listings with things saying "this complies to Ebay policy".
Sandwich: An item not selling in between two items selling (in terms of chronological order, order of number of views etc) OR a item selling in between two items not selling.
Tourist: Someone not from Ebay.co.uk.