I get that it may be a case of not being street smart enough when going or not being familiar/not enough research when visiting Sim Lim that may create that impression that Sim Lim isn't a reliable place.
I have personally avoided. Colleagues told me that they will charge me more because I don't look or sound local. I just took those words of advice.
there are two kinds in Sim Lim Square and most places
Those unscrupulous, especially the infamous phone shops who sell a 100 $ phone for 300 $.
Then there are honest computer shops, who try to make a living by selling a 100 $ graphic card for 100 $. And take care of replacement, repair etc as good service.
Just idle banter, which of the above you need to watch out for ?