Buying a second hand nintendo ds...advice please!

[wellthatsdoneit]

This is what ds would really like to have for his birthday and I can't afford a new one. As he'll be five, I was thinking that maybe he won't know the difference between the 3ds and an older model like a ds lite or dsi - do you think that'll be ok? He has been talking about mario kart 7 though, and I think that's only 3ds, but perhaps he won't know the difference between mario kart 7 and the older mario kart???

I've been looking at them on ebay - can anyone tell me what they mean by a 'refurbished' model? Does this mean it's had the casing or screen replaced so there are no scratches etc?

Lastly, is there a great deal of difference between a ds lite and dsi that a five year old would really notice, and is there anything in particular I need to look out for in buying a second hand ds console?

TIA

Both mine had second hand Ds's at 5. They wouldn't have got them if they'd had to be new.They don't know what type they are (and TBH neither do I).
They also only have previously owned games.
They love them and they're still going strong 2+yrs and 1yr later,respectively.