Obtaining a liquor licence to serve outside customers in Sri Lanka is hard to get and expensive. Please bear in mind that if you purchase alcohol from a business who does not have a genuine liquor licence you are supporting an illegal operation. These people purchase the alcohol from the store and are making a substantial profit as they do not pay taxes or vat.
There is enough corruption in Sri Lanka so tourists can make a stand by only supporting genuine places to purchase alcohol and stop haggling about the Rs40 difference in price.
These places often do not have their alcohol on show & certaintly are not allowed to have the benefit of alcohol company promotions or fridges so you may be served warm beer.
Although there is a fair amount of emphasis about malaria being in the Northern parts I can't say I have come across a malaria area in Trincomalee. Howvever dengue fever is a real problem and that is rife in very urban areas like Colombo. Some areas have more mosquitos then others I have been given tips by other travels that a mix of garlic & vitamin B tablets are highly effective against mosquitos.
It begins with a high fever then a rash, vomiting, headaches, joint aches complete dehydration it is unfortunately a killer and there is no real treatment for it although you should avoid asprin. There is no vaccine against dengue fever so prevention is the ultimate protection.
In Europe 50% Deet Products are recommended although I have found these to be highly toxic in smell and taste. It is far better to buy some non chemical stuff locally like Soffell or Citronella Oil. Some Mosquito coils in Sri Lanka are made from cow dung there are plenty of these in Sri Lanka so they are generally cheap but your room should be well ventilated the smell is a bit nasty. Sleep under a mosquito net at night time, there are definite mosquito breeding seasons so check with your hotel and stay safe.