Importing Gemstones Duty Free
This scam is widespread in Jaipur and also Agra, where many people come to buy gemstones. It's also now occurring frequently in other popular tourist destinations such as Goa and Rishikesh. The scam involves tourists being approached by a gem dealer, who convinces them to buy some gemstones for him, import them under their duty free allowance, then sell them on to one of his willing partners in the their home country for much more money than they originally paid.
Of course the details that you'll be given about the "partner" are fictitious and you'll be stuck with a lot of worthless gems. Definitely avoid anyone who approaches you with an offer like this or any similar scenario. More recently, there have also been reports of scammers posing as fellow travelers, so do be aware of anyone who tries to befriend you anywhere in India.