Not here to defend TCW or anyone but its always been buyers beware!
Legally speaking, you as consumer have the priority to prosecute TCW. Because as customer, if I buy anything new, I expect FULL ORIGINAL warranty back up from the brand office. Which means to say, Sigma product purchase from ANY SHOP, should be able to be received by the Sigma office here in Singapore, for any service and repair.
Actually, you do not have priority. Sigma or any other company will always tell you to get a shop from their AUTHORISED dealers. TCW did not advertise themselves to be as such, no posters or anything, so you made the assumption that they were authorised.
Shop thats practise parallel imports MUST disclose such info to customer or they could be prosecuted for "MISREPRESENTATION".
Actually, shops are not require by law to disclose their sources. MISREPRESENTATION only comes into effect when they blatantly promised you something but gave you another. Ie: Used lens sold as NEW. Or if they mix gray and official stocks together and sell them as the same thing. A grey set is new, it just isn't brought in by the distributor.
Although parallel import stuff can be cheaper and does attract more buyer, but theres' always tonnes of inconveniences with regards to warranty, which ultimately the customer themselves have to bear.
As a customer, I'll not take it lightly that TCW can take things for granted and "PRESUME" customer show know theirs are parallel imports. If thats the case, TCW should also "PRESUME" that they can be sued and prosecuted any time.
I won't comment on the the inconvenience bit beyond that in my opinion, a spoilt lens, whether serviced by sigma or TCW is still an inconvenience. True, as a matter of practice, TCW should not assume that customers know their stock is gray. But as pointed above, they didn't MISINFORM you either. It is just bad practice, and i am surprised they didn't tell you as even as an old bird there, they still tell me all the time, right from day 1 that i went there. As for sueing them and prosecution, you could file a complain with CASE and they might get blacklisted by CASE but beyond that, i doubt you have the law on your side. Bringing them to court could backfire into a case of them sueing you for discrediting and defamation, which is more costly for you!