I used to rescue rats that had been treated just terribly and were very badly behaved and I never had one not come around eventually. Rats are very curious and social and usually that wins out over fear eventually if you have patience and build trust. Here are some steps that I would recommend, that have worked for me.
1. Look them over carefully and listen/watch for any signs of injury or illness. Petstore rats are more likely to have untreated health issues and a rat that doesn't feel good can be much more prone to defensive behavior.
2. Bribery. treats, food, toys, whatever works. Make sure you are associated with all the most wonderful things in life, esp. fruit or peanut butter flavored yogies, food of the gods.
3. Get them out of the cage by whatever means possible without actually forcefully pulling them out and terrifying them. You can try just leaving the cage door open and see if they will wander out or lure them out with more bribery. A lot of rats that have not been handled much by people and kept crammed together in too small petstore setups can become somewhat cage territorial and get fearful when you reach in the cage to interact with them. Sometimes these same rats behave much better once they are out of the cage. If that works then you can work from there to being able to reach in the cage after they trust you and have let you handle them a bit.