Results are very variable.
Be sure to distinguish between high cost suppliers and high cost brands.
"Provenance" is a major factor.
If you can trust the manufacturer AND the distribution channel then you probably know what you are getting an can decide if it suits you.
If you cannot trust BOTH of these you have no certainty that what you get is good BUT a reasonable expectation that it is not.
Components supplied by reputable manufacturers own outlets are trustable
(at least often enough that only paranoia will save you if they get it wrong)
Components sourced by reputable suppliers are almost always trustable.
eg if you see a brand offered by eg Digikey you can expect that versions sold by them probably are from the manufacturer claimed and probably have a data sheet and probably meet datasheet specs. You can also expect to be able to buy many of the same genuine products elsewhere for somewhat less than they charged, and apparently genuine but actually fake products elsewhere at unknown prices.
Buying Panasonic parts is always a good idea and they are often not much dearer.
I have no business relationship with Panasonic except as a satisfied customer.
They make a wide range of products and seem to know what it takes to make quality product - and then choose to do so.
(Wet aluminum) Electrolytic capacitors are useful products with well defined designable lifetimes IF you can rely on their specifications. From "unknown name" manufacturers I have seen "105C rated" caps that were poor examples at any temperature and others which you know are not up to spec just by looking at them. Others are not so obvious.
A significant percentage of Asian electrolytic capacitors are low spec and data sheets are rubbish (based on my having used many hundreds of thousands of ecaps in designs made in China and so having looked carefully at what is offered.) You can get some entirely acceptable ecaps from Asia - but if you are buying directly from Asian suppliers you must be aware of possibilities. This only applies to volume production. For small quantities rely mainly on a reputable supply channel having been vigilant for you.
A failed 0.1 cent resistor can destroy a product.
1% resistors from reputable suppliers in modest volumes cost so little that insertion costs predominate. Buying from sources where you are not aware of provenance makes no sense at all.
If you find a product frm an unknown manufacturer and you are uncertain about the supply chain and there IS a datasheet but it leaves you in doubt - then quite often it can be useful (end enlightening) to take a "likely unique" phrase from the data sheet and do a web search for it. If ALL examples are from the manufacturer concerned it tells you little. BUT often enough I have found that chosen phrases turn up in a range of data sheets fro related or even quite different products from quite unrelated manufacturers.
If you get a technically highly competent sounding comment in an apparently less than top-class data sheet you will often find that it has been "mined" from the data sheets of a top class manufacturer. At one stage I did quite a lot of this sort of searching and found that such copying was common enough from suspect specification manufacturers to make the searching worth doing. [I often did this because a manufacturer named a given brand part that they intended to use and I wished to demonstrate the desirability of using the parts and brands that I had specified. Saying "just do it" may work, but being bale to say "because ..." as well may some times help. Sometimes.]
Unlikely but apparently true from what I've seen :-) : LiIon batteries with "Fire" in the brand name may perhaps be OK from genuine makers but seem to attract cloners who wish to claim ver higher (often impossible) mAh ratings. [Ultrafire, EverFire, SureFire, ... :-)]
Small user replaceable batteries (eg AA C D) can usually be checked by their weight. A light for spec battery is always fake. An OK weight battery may be fake - but probably will be OK. Any AA Alkaline or NimH under 25 grams should be looked at with care. Any AA claiming over about 2700 mAh similarly. 18650 LiIon cells claiming over about 2300 mAh - look carefully. 2500 mAh may be possible. You can get 18650's labelled as 3000 3500 and 4000 mAh capacity - walk away ... .
The majority of smaller Alkaline and NimH cells come from 3 major Chinese manufacturers. Two usually do not sell retail versions under their own names. GP or GoldPeak do - and they are good enough that there are many fake/counterfeit imitations on the market with their labelling. I have seen Sony branded batteries whose labelling and packing pass very close inspection - but whose weight instantly marks them as fake.
FWIW - semiconductor components made by Chinese manufacturer LRC (Leshan Radio Company) that have a specification the same as OnSemi parts are (in my experience) trustable and essentially identical. LRC and OnSemi at one stage had a joint venture operation. Whether this is still in force I know not but their product seems solid - mainly older tech parts.