They're everywhere, con artists, frauds, crooked taxi drivers, and such. When you're an expat or aspiring expat, they're particularly daunting. Lack of knowledge of local prices, rules, and customs can make you an easy mark.
Perhaps, if we share our experiences and stories, we can learn from each other's mistakes and help each other identify scams before it's too late. We can also explain and share stories about things that look and sound like a scam, but really are legitimate ways in which things are done here.
I'll start with a taxis...
I take taxis enough to know the prices between point A and point B at different times of the day and different traffic levels. Normally, I feel relieved when I find a taxi that has a functioning meter, so I don't have to overcome the gringo price bump taking a taxi across Quito. Unfortunately, some taxis are getting more sophisticated with their scams. On more than one occasion I've seen "fast" meters where a $2 ride came to $5 or more on the meter. Not a huge deal, but if you're taking a longer ride, it could really add up. So far I haven't seen anything as scandalous as the taxis in Istanbul, where a bump of a radio knob might also bump the fare $20.
My advice in Quito is to try to stick to the black and yellow cabs, as they seem to be the least shady. If a taxi has no meter, negotiate a price first. Also, if you try to hail a taxi, and you get some random guy driving a car that is obviously not a legal taxi, don't freak out. Use your judgement. I've taken many not-a-real-taxis and paid reasonable prices. I also recommend trying to quickly get a feel for and memorize what a $1 taxi ride is. If you ask the price for a short ride, you're letting the driver know you're new to the area, and inviting him to overcharge. It's better to assume the ride is only $1 and confidently hand the driver just that. If it's short, he'll let you know.