Missylan,
To pursue or not it's ultimately your choice, but of course if suay suay (touch wood) the re-tiling work is worse than original, then it's really at your own expense... unless you have all the time in the world to make them rectify until you are satisfied...
Wat I understand is that the lippage and flaws are more obvious for those who chose marble, cos it's light in colour and the lippage is extremely irritating to the eyes during the daytime when the sun shines in. Actually my tiles are also uneven (and my blood boils whenever I feel them with my fingers), but I told myself to accept in and try to live with it...like wat Merci has suggested, maybe can put a carpet to cover up the imperfect tiles and you won't be reminded about it as often.
Merci,
I think the marble tiles they used are very thin (lousy ones) so maybe cannot do hard polishing to even out the lippage, as the polishing will cos the tile colour to change. Think what they will do is only buffing to improve the shine that's all.