Sugar gliders aren't nice by nature. In other words, if you saw one and went up to it, odds are it would either run away or lunge at you.
Even when bought from a good breeder, chances are that a sugar glider will not like you right off the bat. Which is why you need to spend so much time bonding with them. The recognize people(and other gliders) by smell. So, once they learn your smell they will become more comfortable with you.
My gliders are all bonded to me and I can pull any of them out of their pouches without a single crab or bite. Some of them, like Milky Way and Leda, I got when they were older(over 2 years old), so they aren't as well bonded to me and won't come up to me and cuddle, but they trust me enough to no longer lunge and crab at me.
My younger gliders, such as Silvara and Gilthanas, with groom me whenever I play with them and they like to use me as their personal jungle gym.
Then you have the joeys, who I have handled from day 1, so they're so comfortable with me that they fall asleep in my hand, love their bellies rubbed, and if they get anywhere near the neck-opening of my shirt they'll climb down and fall asleep in my bra.
It just depends on the gliders individual personality and how much time and effort you put into caring for and bonding with them.
They're high-maintenance pets and their diets are extremely difficult. Get it wrong and they'll slowly get sick and die, get it right, and they'll live 10-15 years.
They need fresh fruits/veggies/main diet(special mix you have to make by hand. I make HPW). They're messy, can be smelly, and are noisy(they bark like a chihuahua at night).