HDB shop rental is usually, if not always, by tender.
whoever puts in the highest bid usually get the shop.
nothing to do with MPs.
i wonder why though, and if there's a better way to do this. price should not be the only consideration. if Sheng Siong, or Prime or Budget Value etc is good to have in Punggol, then rental should be lowered to subsidize the business such that the business can survive and residents are served. higher rentals just go to HDB, and the high rental costs are passed on to residents. when the rental is too high, we have business failures, and residents have to go without the service.
going by lowest price however.. is the safest way for civil servants to conduct business, stay safe, and keep getting promotions and salary increments. and probably less chance of corruption.