I would say that unless you have a friend with a script
don't tell them you do .
Never say something you can't follow through on.
If they don't have any [direct] reason to think they're yours you tell them:
Nothing Yup, not a damn thing.
It a damn site better than lying and then having to not only remember what you said, but you'll always have to come up with more to fill the wholes in the first lie.
There's not too many who can do that well [though I've personally met one who could; thaat boy could talk the tits off Christina Ricci - no, don't ask

].
Backing up...
If you don't say anything - or deny any knowledge of them then the burden of proof is on them to prove that they're yours or that you did know about them.
If you must say something try to use as much truth as possible - it's easier to keep things straight if you do: the truth's easier to remember.
Do you get a lot of different people even stopping for a second?
If so, tell them that and that it could belong to any of 150 people.
Was your room cleaned up much from the previous tenant?
say they must have been there since you moved in.
Bottom line: unless they can directly say that it's yours: deny, deny, deny.
I almost forgot;
[Make sure you don't have anything in your system first, then], if they keep pressing you, turn on the offensive:
Get indignant:
Demand that they give a piss test, telling them you will expect a written letter of apology from each offender to go into your permanent file.
Remember: The best defense is a good offense

[This message has been edited by Metaphysicist (edited 11-22-2002).]