Seriously a good tiler will point out the mistakes and rectify them . I would also remove a tile to see if there is good coverage if not i would take them all down
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Tell him to put things right before he goes any further as you are quite rightly not happy with his work ,see how he reacts ,if badly tell him to leave the house Pronto and then take things further at least then you have given him chance to make things right and he will be extra careful hopefully
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