I don't really want to write too many negative posts on this site, but I felt this was a problem worth highlighting. Overall, Rome was a real pleasure to visit, and I thoroughly enjoyed my time in the city. Still, the issue of street sellers/vendors is a real one, particularly around the Colosseum. I don't want to get into the politics of why they are selling these items, that's their choice, and I'm sure they have their reasons. The majority were incredibly aggressive though, and I think this is worth highlighting for any visitors to the city. We visited in August of 2020, during the coronavirus pandemic, so while it wasn't as busy as normal, there were still a lot of tourists in the area. We noticed the street vendors almost immediately, with a lot trying to sell tickets to the Colosseum and the Roman Forum. They were also selling water, which can be useful on a hot summer's day, but it's important to point out that there are free water facilities in the area as well.
They were also selling selfie sticks, and chargers from what we saw. I felt that these were quite easy to deal with, just a simple "No" would suffice normally, and they would walk on.
The main problem we had was with the sellers who would try and engage you in conversation, and would not leave you alone. They were quite aggressive at times, and I felt we did well to mostly ignore them. My beard is quite long (I'm bald so I like to compensate), and the usual conversation would go like this: Seller: "Are you African? You have an African beard. Great beard."
We would ignore mostly, and it worked a lot of the time. This article does a good job of detailing techniques on how to deal with the street vendors, and we mostly went with the ignoring technique (the article advises you to be rude, but I'm mostly too nice for that). There was one time where we had to stop though, and a particularly aggressive seller approached us. There was the usual chatter about my beard and where we were from, and he kept trying to pawn items on us. In the end, he actually threw a bracelet at my girlfriend, in the hope she would catch it, and he would force her to buy it. It actually bounced off her, and we just kept walking away. This bracelet technique is quite common, where they tie it on you, saying it is no problem, then they charge you for it. It appears street selling is illegal, but there were still plenty around the colosseum, despite a large police presence as well. We found ignoring them was our best bet, and it worked well for us, but it is worth being vigilant during your visit to Rome. Try not to let them intimidate you, and if you do need something, you should find lots of alternatives in the nearby neighbourhood. They didn't spoil our trip, and there is no reason they should spoil yours either. Stay safe!