It's very easy to destroy these ah beng shops.
All you need to do is ban them from offering any kind of warranty, paid or free. You can be a reseller but to get a warranty you'll have to register with the manufacturer with the invoice information.
In other words, the same warranty policy as when purchasing computer equipment.
Slim margins and high rents... they'll just shrivel up and die.
Unfortunately, because Singapore is such a basket case these days, once these ah bang handphone shops fold up, they'll most likely be replaced by tuition centres ('approved by MOE' and with outlandish claims), pawnshops, moneylending shops etc. If you're lucky, you may find a Sichuan eatery or a maid agency.