I lived in Riga for 4 months and hated it.
Girls are pretty but very unsocial, many try to scam you, and in some nightclubs foreigners are overcharged. Indeed, they whole country is a scam.
Be careful about girls asking you to join them for a drink, it is a common scam in the downtown. They work for the bar.
Always try to pay in cash, rather than with a credit card, and if you pay with a credit card take the TPQ with you. Do not let them charge you without seeing the amount they pay in the machine.
Prostitution is declining, due to restrictions, although technically legal.
There was a nightclub, Studio 69, you could pick up girls there. It is for the Russian-speaking community, which is about 50% in Latvia. The top part is for +30, while the lower part (The Rock) is for a younger crowd.