It's a paid service. Supermarkets will push certain products for a fee, and employees also earn commission for each article that gets sold (or sometimes they're just part-timers hired for the occasion), thus becoming a proactive source of annoyance. You know, even the good spots in the stalls are for rent. It doesn't mean the products are particularly good, or bad though. It just means the company paid for your harassment. 

And since this is China, no shit is given whatsoever whether these methods are in fact  ruining the whole experience for... you know... the client.

I avoid supermarkets like the plague. Buy from the internet.

Frankly, with so many toothpastes, soap, and god knows what else, I pick at random half the time anyway, so I always go with the suggestions, since I don't care.

In the supermarkets, some brands will have their specialized stands and the supermarket has some part-timer promote the brand for a commission fee. I had a Chinese friend who once did this. 

In the restaurant situation, I would suspect the same thing as you. 

I usually know what I want, especially if it's in a supermarket. I find it irritating when someone tries to force their product on me.

Same with buying clothes, if I'm browsing the shirt section for example, and I don't pick up the hideous lime green and purple shirt for a closer look it's because I don't want it and people who keep telling me to try this, this, this just make me go somewhere else.

I mostly avoid any recommendation here, for the same reasons. it will not benefit me.

What I do really love most, is when I enter Auchan or Carefour stores, and around fridges  with icecream or meat and veggie stalls are some ladies with speaker and microphone and try to sell out things. they are ussualy 5 or more of them, and of course, they sell each something different. Because one have to listen clearly, what she offer, the poor quality speaker is on his highest crappy volume, so the other women should do that too, let people can listen what she is selling. This is my nightmare. this is crazy. Once I came and aproach that lady, turned the volume button down and told her "please lower voice". she was surprised, people watched me, but all others failed to turn volume down.  

I usually politely reject the assistance in supermarkets as I usually know what I want to buy with the exception of asking what is in action (therefore I already have two big shopping bags which were added to the goods for free ).
In restaurants I never follow waiters recommendation due to the very simple reason - my taste differs from majority of my Chinese friends around me. For instance I rarely eat chicken as I hate the bones splinters but majority of Chinese finds the meat without the bones not as tasty as the one with the bones.
Just in case of very simple menu which does not provide any ingredients information I ask what is hidden behind, sometimes, extremelly colourful names.

Know what I need, and avoid all "suggestion"

I just buy what is good and what works. In China, when you find that you never forget it because everything else (60-80% of the rest of the stuff) either breaks, or has low quality. 

Do I listen to the people giving suggestions? Hell no! 

Think about it for a moment. They were born here in China! They are used to low quality goods and can't really tell the difference... whereas YOU come from a country where all the high quality goods are exported to and have lived your entire life. 

So go with your own gut feeling because you are probably an expert already. When it comes to Chinese food though... trial and error is necessary. 

No never but I enjoy wasting their time, I only go to the shops to try on clothes, I let them think that I will buy a lot of goods then at the end I thank them before saying that I will buy online because it's cheaper. This drives some sales people absolutely mad.

I never ever follow sale assistant advise, simply because they do not know my tastes. One can buy 10 items of clothing in a store and they are never happy, they want you to buy 10 more, and everything is made just for you, even the  zig-zag striped jumpers, or if your highway patrol 'pullover' what about the dazzling shirt full of sparkling thingies, coats with fur collars. They'd sell their grannies just t et a sale. Same applies to restaurants, I eat what I want, not what they what to sell me. What does annoy me is when they tell your wife to ....get t foreigner t buy it' and we'll give you a gift. She replies 'the foreigner' is my husband and he understands what you say,, talk about loosing face.

I was a chef a few years ago. When a restaurant has a "special" it is usually something that has been sitting at the back of the fridge for the last couple of weeks - unloved and long forgotten. The only thing "special" about it is the fact that the kitchen is desperate to get rid of it and that it has a dangerously high bacteria count.

Anything they suggest will be the LAST thing I would choose to buy!

I can't understand them when they make recommendations, so...