1st of all, I think the mod chip is call merssiah or something
like that. Last known is merssiah2 i think.
And if i din remember it wrong, the mod chip is illegal now.
Things to look out for are, how many original PS2 controllers are u
given. Memory cards ?
To be on the safe side, bring a priated ps2 game there to try on
the set before you pay for it. If it cannot play, then its nor
modded for pirated games.
In case they claim , " oh must be your this dvd spoilt, thats why
cannot play. Bring 2 pirated games 
Have fun. Btw. why not you wait for the release of PS3 ?
There price of brand new PS2 will drop... and people will sell
their PS2 when they upgrade to PS3