Quinta Avenida is jam packed with shops, bars, restaurants, and things to do. Many of the shopkeepers will try to get your attention by calling out to you about deals or how good their merchandise is. It's fun to barter for a deal on merchandise with them but remember if you can't get to the price you want, the guy next door has pretty much the same stuff so try there.
Lots of the people sitting outside shops will try to sell you drugs or say they know where you can find a prostitute. After dark, the prostitutes hand out business cards by the clubs. No one was pushy about it - just a polite 'no, thanks' and they'd leave you alone. Probably not the best place for little children but maybe the offers are tamed down if there are kids around.
Personally, I loved the energy of the place. No one stuck me as dangerous and everyone was welcoming. Most everyone spoke English and those that didn't found someone close by that could.
I'd go again without question.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.