This regulation is started by making aware to authority by complaining of such malpracticing.

Some OTC drugs in the USA such as pseudoephedrine have quantity limits when purchased. This API can be used for synthesis of methamphetamine, hence the limit.  

There should definitely be tighter control of not just OTC drugs but also of cosmetics and food products which by definition contains 'drugs' in the sense that they contain chemicals capable of interacting with body targets to modify biological functions. Worse case is when OTC drugs are sold in supermarkets and without supervision by  a pharmacist users get the wrong impression that they are safe.

It's difficult and probably not practical especially in developing countries where drug distribution systems are mainly chaotic & prescription practice is poor. 

In Nigeria the regulator through pharmacovigilance & effective PMS engages in reclassification of some medicines with very high incidence of abuse.  In 2012/13, all cough syrups containing Codeine were reclassified from OTC to POM. This classification not withstanding, POM medicines could still be freely bought off the shelf without prescription.  This is due to systemic weaknesses in healthcare delivery. 

In developing countries where the regulations can be easily broken, the key person on medication control is the pharmacist himself who should have the required knowledge, skill, care, alertness , honesty and humanity to control the dispensing of medication and avoid dealing with an authorized medications or to give POM to those who do not need it without prescription and to instruct the patient on proper use of medications and to avoid medications of doubted effect and unknown side effects like slimming agents, sex enhancers and some cosmetics

best regards

In developing counties its a major task or challenge to country system ,

NGO  or Government  should CONDUCT several awareness events like need for Community education for rational use of Drugs and Pharmacovigilance.

Regulatory officer and pharmacy council have important role in monitering  Pharmacist service and  play  value based service in this regard. 

Sale of drugs should be STRICTLY under  Drug Rules of the country .