Long gone are the days when one could criticize Twitter for being a revenue-less startup without a business model. Today, Twitter does have a business model, and several commercial offerings.

One of those commercial offerings: Promoted Trends, which gives brands the ability to insert themselves into Twitter’s Trending Topics list.

Given the prominent names that are purchasing Trending Topics, it would appear that Twitter has a decent revenue stream on its hands. While it may not be that big relatively speaking, it’s a start.

But Twitter, and the investors who have poured big bucks into the company, probably shouldn’t start thinking monetization isn’t a big deal anymore. That’s because if Promoted Trends are any indication, Twitter has a lot of work to do on the commercial front.

The other day, Verizon ran a Promoted Trend promoting its 4G network. But the Promoted Trend didn’t just promote Verizon’s 4G network; it promoted spam, as can be seen in the screenshot below:

Most of the links — the ones that worked at least — took users who clicked on them to sites offering free 4G phones:

Needless to say, this is probably isn’t what Verizon had in mind when it decided to run a Promoted Trend. Although Verizon’s 4G tweet received significant exposure, the wireless carrier’s Promoted Trend essentially served as an even bigger promotion for an incessant stream of spam that had one goal: dupe Twitter’s least savvy users into thinking that they’re getting a free or low cost 4G phone — from one of Verizon’s competitors no less.

Verizon should be disappointed, but Twitter should be embarrassed. While there’s no doubt that dealing with spam can be a difficult task, when I watched as dozens upon dozens of spam tweets flood in every few minutes for Verizon’s Promoted Trend, it became apparent that Twitter has little will or ability to stop spammers. Which is somewhat curious, given that most of the spam tweets had largely the same text and seemed to be posted by bots at roughly the same time.

Twitter’s inability to deal with spam, particularly on a Promoted Trend that a major brand ostensibly paid decent money for, begs the question: will Twitter ever produce a commercially respectable advertising product? It has the reach, and perhaps even the right ideas. But when it comes to execution, it’s hard not to conclude that somebody is asleep at the wheel.