Glyn Roberts, of NIIRTA, spoke to UTV after a third consecutive night of trouble in the east of the city.
Trouble broke out in the area when hundreds of loyalist demonstrators returning from a march to the City Hall came under attack from missiles thrown from the nearby nationalist Short Strand area. Police are investigating reports of shots being fired from the loyalist side.
The protest march over the flags issue passed off without incident. However, the presence of up to 1,000 loyalists resulted in road closures, and major traffic and trade disruption.
Riot officers dealt with disorder in the Newtownards Road, Albertbridge Road, Castlereagh Street and Templemore Avenue areas for several hours on Saturday.
Protests, along with street violence, have been taking place regularly throughout Northern Ireland since Belfast councillors voted in early December to only fly the Union Flag from City Hall on designated days.
Mr Roberts appealed for those behind the rioting to put a stop to it.
Condemning the violence, he said: "I would appeal to the people organising these riots to stop - consider the damage they are doing, not just to their own local community, and their own local traders - but to the reputation of Northern Ireland throughout the world.
"We've international TV crews here covering this - beaming those pictures of riots across the world. That's doing immense damage to Northern Ireland's reputation at a time where we're desperate to get foreign, direct investment.
"So I appeal to the people behind these riots to stop and consider the immense damage they are doing."
The retail expert added that it was not just Belfast city centre that was suffering, but small retailers located in the city's arterial routes.
"Traders on the Newtownards Road, on the Albertbridge Road were pretty much unable to open yesterday - and people forget about those small traders as well.
"Both those areas have a real serious economic problem. There are many shop vacancies there and these continual riots certainly don't help those traders."
He described the protests as "counter-productive," stating: "They are damaging their own local communities."
On Saturday night, eleven men and two women charged over rioting in Belfast appeared before a special sitting of the city's Magistrates' Court.
Four others were also charged at other court sittings on the same day.
Meanwhile, nine police officers were injured on Friday night during rioting throughout the Greater Belfast area, while 10 received injuries on Thursday night.