As mentioned above, look for the engine code, as well as listed on the data sticker in the boot/service schedule there should also be a bar-coded sticker on the plastic cam-belt cover at the front of the engine, this also has the engine code printed on, the 110 bhp engine is AFN code, think there are a couple of codes which are 90bhp's, 1Z is one type....
The 110 bhp models also had a TDi tail badge where the 'i' has a red flash next to it, though that can't be taken as gospel as someone could have put another badge on!
The later 110 bhp engines have an engine cover where the 'i' in the TDi logo is again picked out in red but this does not apply to earlier 110 engines, where it is all black...
Best bet really is the data sticker,failing that the vehicle V5 will list the engine number and code, can you ring the seller and ask what the code is?