In shopping malls/complexes, break-ins also take place through false ceilings and through the floors of vacant/ unattended shops above/below.
Usual break-in happen thru the back door or ventilator or exhaust fan opening or by removing a AC. It is also not uncommon to break the lock on the shutter or to just force open the shutter out of the channel by using a crowbar. Most of shops in a market have a common Guard, who is normally underpaid and ends up doing more than one shifts of work. Due to this overwork, the guard also ends up sleeping once the activity dies down, giving the opportunity to the thieves.
Depending upon the location and construction of the shop there are many possible weak spots that you can judge for yourself or seek professional help for an Security Audit. Do not under-estimate the innovation capability of thieves.
Sometime back in Delhi , a criminal entered the sewage line through a manhole close to a jeweler's shop and reached below the shop floor after digging his way through for five days. Unfortunately he lost sense of time and started digging up wards to break through the shop floor during the shopping hours and was thus caught in the act by the alert shop owners/staff.