The guy is most likely screwing you.

 

From what I'm to gather "CI" is Common Interface, which I'm pretty sure the DS doesn't have. He probably was misusing the term to mean the NDS' Slot1 (NDS Card Slot).

However, that doesn't change the fact that the AceKard shouldn't be damaging that slot.
The AceKard is actually THINNER than retail NDS cards and other Flash cards which leads to a contact issue (where the card isn't making a good connection). This can be solved by slipping paper behind the card or trimming a small strip to fit under the contacts.

All slots for games have been keyed in every hardware released by Nintendo (meaning they only fit in ONE way) so jamming the card in 'backwards' is impossible. I'm not sure how it would have been damaged by ANY cards let alone the AceKard. Though I have heard of someone snapping off the 'teeth' of the AceKard, even that is beyond me to fathom how they did it.


I'd be interested to find out if he actually changed anything... but that would require you to open up the DS and take a look at the slot which I'm sure not everyone would be willing to do. If the Slot looks attached VERY cleanly (all the soldering looks perfect) you can bet it wasn't touched -- AFAIK even a skilled solderer can't match precision of a machine.