Yes,its good to be careful, and be alert to the fact that scams exist. When dealing with uninvited contacts from people or businesses, whether it's over the phone, by mail, email, in person or on a social networking site, always consider the possibility that the approach may be a scam.
Also now who you're dealing with. If you've only ever met someone online or are unsure of the legitimacy of a business, take some time to do a bit more research. Do a Google image search on photos or search the internet for others who may have had dealings with them. If a message or email comes from a friend and it seems unusual or out of character for them, contact your friend directly to check that it was really them that sent it.