Unsolicited sales or donation at HDB flats after office hours

Lately there have been several visits by salespersons or "volunteers" soliciting donations (hereafter will be termed as solicitors) to my HDB home at private hours (e.g. 7 pm to 9 pm where we would be having our dinners). There was one occasion when a solicitor rang our bell and knocked on our door at 10 pm.
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First of all, I would like to say that such action by them are unwanted and annoying. Secondly, I will not contribute a single cent to them mainly because of their inconsiderate action (e.g. encroaching our private time to have uninterrupted dinner especially after work), regardless of what they are push-selling (or push-marketing). For families with 4 months old babies and an unpleasantly loud door bell (which we never got the time to change), having someone pressing the door bell repeatedly can make your blood boil when babies started crying out from their slumber. One thing I suggest doing is to buffer your door bell with cotton balls (which worked for me).
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Let me tell you about my experience with these solicitors at my HDB neighbourhood.
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1. Ice-cream students used to coax HDB occupants to buy their products. It worked initially (and I bought some) but after the frequent visits, the trend probably died with dying demand (because I have not seen anyone of them knocking on my door anymore).
2. Donation solicitors with improper attitude and sometimes appearance. The ways they approach the subject of donation are akin to asking for fees. I got one that irked me tonight. He rang the bell and then knocked incessantly on my door. At time like this having a "legit" warning signage such as below would make my day.

   

   You can buy it at The Patriot Post Shop

3. Singtel salesperson push-selling broadband service at our home is mind boggling. Why would an established brand such as Singtel go door-to-door soliciting subscriptions?
4. Great Eastern insurance salesperson at my door step during dinner time is like asking to be shooed. What is worst was that he came back ringing my unmodified doorbell (i.e. prior to stuffing cotton balls into the darn thing) and woke up my baby at 10 pm later.
5. There are plenty of others whom I did not bother to greet them at the door step. Those who are smart will not bother to ring my bell or knock on my door. However, the one who did incessantly knocking on my door was the guy with bad attitude and appearance (see point #2). I can only try to guess his odd and inconsiderate behaviour.

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Now, we must be asking the same question right now. Are those solicitors who knocked at our HDB doors are doing something legit? If private homes such as condos can afford to have securities protecting them from unwanted solicitation, what do HDB occupants have to protect them from such unwanted solicitation?
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What is not cool is that there are some HDB occupants who motivated such trade by buying into their solicitations, e.g. products, services, or donations (I'm assuming that these donations are legit but I am sure there are also those belonging to scams). These gullible customers are doing disservice to other HDB occupants because once there is motivation sparked by sales and profits (or positive response), many others will be jumping on the bandwagon to start "pushing" their trade to other HDB occupants. Be prepared to answer more door bells and knocks if that ever happen.
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