I've been living in Riga for more than 4 years and have never had a problem. In any case, yes, there are places that will take advantage of you.
As soon as they hear english being spoken, the cash registers in their eyes light up. Sorry but I've heard nothing positive about any of the places in Riga. They are all out to swindle you. Reserve well in advance, esp if large group. Do me a favor and leave a small donation, the place needs it. First thing to do after getting off the plane is picking up a copy of the magazine 'Riga in Your Pocket' - just about the best guide to Riga available. A guy was thrown in jail for 5 days for urinating on the freedom monument.
If you need a toilet, just go to a hotel, they shouldn't give you too hard a time. There is a bus from the airpot to the center you can take, as well as a shuttle bus that takes you to the Hotel Latvija but doesn't have many seats.
Riga is so small that unless you are staying somewhere well outside the center which is probably unlikely anyway you should never need a taxi. I'm an American who's been living in Riga for about 4 months. Generally I don't have problems with the taxi firms, the red taxis near the laime clock work for me when I'm too lazy to call Taxi SOS - the cheap taxi service.
Then again, I speak perfect latvian, so that could be a reason the taxi's don't rip me off. I second not going to the strip clubs, full of criminals. Avoid the prostitutes, maybe it's a personal thing but it's a tremendous risk to bed a prostitute in Riga, enough of a chance you will get robbed or get an STD. Don't talk to the locals on the street. I usually say not to go to club essential as well. I've had a good time there but it's full of prostitutes and you need to watch out there. I speak a smattering of Latvian but usually the locals detect my accent anyway.
