I personally have not had to send anything back, but if ever folks in the USA send them to GWInstek USA; they've been there since the early 1990s. For other countries, they are big enough to have branch offices so it probably helps to buy it wherever a local branch exists.
http://www.gwinstek.com/en-US/Page/About_Instek_AmericaTheir target market has typically been trade schools and production facilities so durability and quality has been a key feature [ you can search any of their products for reviews in Amazon] but they have always suffered in performance/price against competing models with specific features. Most importantly, if the data sheet says it does XYZ, you get XYZ.
That said, you should always buy based on per model evaluation, not brand name. On this particularly thread, I presume you inquiring is about the 1000B or 2000E series, which are quite different from their previous line up.
I didn't see anyone mention "service" (or lack of). I can only speak about Spectrum Analyzers, but I would steer clear of Instek.
First off, unless something has changed radically, recently, nothing is serviced here.
Second, YOU have to pay for shipping to China both ways by CHECK, credit cards not accepted. (again, unless something has changed)
Third, At least as far as their SA's, they are years behind the competition, performance wise. (probably why you almost never see any)
The above was from 1st hand experience. ![Wink ;)](https://www.eevblog.com/forum/Smileys/default/xwink.gif.pagespeed.ic.cldandycH0.png)