This horrible trap still happens in Vietnam. Not often, but enough to make you consider it. There are quite a few highway-side restaurants across the country that have deals with certain bus drivers working for low-rated travel companies.
Between cities, the driver will stop at a specific restaurant for a “quick bite to eat”. Once all the tourists are inside, the doors are locked and everybody is asked by a few threatening bouncers to consume something, usually expensive. Travelers are forced to buy foods that are typically eight times as expensive in other places.
Several times, the bouncers use force, while the restaurant owners have agreements with local police officers patrolling the highway.
How to avoid: the best way to avoid this is to always use the most reputable travel companies there. With the advancement of technology, you have no excuse for not finding reviews online about the best way of transportation, wherever you are traveling.