Nope. The shelters know their dogs. Most dogs that are fostered are ones that have been through a behavioral assessment and are totally fine. They just need a place to go. I trained an Anatolian Shepherd who was terrible in the shelter because his breed was a guardian and being surrounded by "predators" had him on high alert at all times. I fostered him for a few weeks and he was the sweetest loaf. He was adopted shortly thereafter.

Another answer to your concern would be the short-term fostering. The shelter isn't going to put you with a dog that has big issues, but if you're still unsure, ask to take a dog out for a trip to Starbucks for a pup cup, or a walk around a new park. You can gradually work your way up with a longer field trip, then a sleepover, and then a weekend foster. Just take it at your own pace and know that you have an entire shelter there as support should you need it.

No dog is perfect. They all have their own personalities and quirks. The best trained golden retriever has likely destroyed a shoe or went counter surfing a time or two. The brilliant thing about these kinds of fosters is that you get to know this awesome new friend without having to commit yourself to months or years. When the dog returns, you can let the staff know some of those quirks and they can work on them with the pup to help make them more adoptable.