Terracotta floor tiles installed in new build are shabby and need cleaning.

you need to wax them. There is a special wax/sealer for them

You have stated that the floor needs resealing does this mean they have been sealed ?if so the best way to remove the sealer is with Nitromors stripper I have used this a number of times on Terracota and works well then reseal after this do not walk on floor while it drys as this will leave footprints and you have do it all over again.

check out a company called exstensive.you will find them online.they do sealers and cleaners and will point you in the right direction.