in my opinion yr ID is pretty honest.
Most ID here in Spore are in for a killing, HACKing flooring and stuffs are their best income !
On overlay over existing flooring, there are mainly 2-3 points to note :
a) making sure the existing does not have a history of water-proofing issue..... with yr frd down-stair !
b) u will have to remove doors to trim the bottom to fit the extra thickness.
c) good contractor needed to avoid tiles poping in future.... not just workmanship...but also the cement used !