Collectors, be aware! Mass production of paintings from China? It's all but art
Chinese art factory - mass production of low quality paintings
If you read the original article of how this paintings are produced you'll see yourself why I say that it has nothing to do with art
Turists, be aware! Fake watercolor and oil paintings in Piazza Navona, Rome
Not only artists in Piazza Navona, some are simple vendors of real or fake paintings. In fact, the oil painting in Piazza Navona you want to buy may be a cheap Chinese copy, while the "watercolor painting" may be a print. OK, there may be real painters with real paintings, too. Anyway, if you like this kind of paintings, check well before buying!
Please note that I have a great respect for real street artists, as I understand their difficulties (I occasionally do street painting, too and I like it but it is a hard profession). On the other hand I do not support fraudulent people.
Read Tripadvisor forum here (in English)
see the video of Roma Corriere (in Italian) here