I've stayed in nearly 100 hostels on 4 continents - here are 9 red flags to look for before you unpack your suitcase

• A hostel can be a great place to stay on your travels.
• But it's hard to choose a good hostel before you arrive.
• A traveler who's stayed in nearly 100 hostels, and worked in one, explains how to tell if the hostel you chose is safe, clean, and a good place to stay - or not.

For millions of travelers, hostels are the preferred choice of lodging.

The benefits are obvious: Hostels are generally inexpensive, conveniently located, and a great way to meet other travelers and share recommendations. As long as you don't mind sharing a bedroom and bathroom, they're the perfect place to stay when you're on vacation.

But hostels can range widely in quality. I would know - I've stayed in close to 100 hostels on four continents, from an uber-fancy, palace-like hostel in Paris to a $1-a-night gem in Hanoi, Vietnam. I even spent one summer working at a hostel in New York City.

While most hostel experiences went off without a hitch, I've also learned the red flags that scream "avoid this place."

Here are nine red flags to watch out for before you unpack your suitcase: