Nicaraguans have no problems with Americans living in Granada. If you treat people well, they get back to you very nicely. If you pretend to be smarter than them, they will not help you or they will not go with you. How you treat others is how you are going to be treated.
Nicaraguans do not discriminate so expats are treated just the same as locals are treated. We go out with expats and do business with them. If you help and you are a good person, people are going to notice right away and will appreciate that. However, just like anywhere, there are people who will try to steal from you and you have to be cautious. There may be some people who will try to take advantage of you and another Granadino (a "Granadino" is a person from Granada) will warn you not to hang out with these people.
I have a friend, Darrel Bushnell, who is the best example of someone who tries to interact with the local community here. He is a person who teaches and motivates people to do well and make something out of themselves. He always talks with Nicaraguan parents, he play movies every Friday, and people love him because he is very nice but he never gives things away. He always makes people work. Whenever you do him a favor, he will give you something. Just like anywhere in the world, if you treat kids well, and you teach them, people will notice and they will appreciate what you did.
Parents in Granada are very conservative. So they love to see you interact with their kids. They also pay attention to be sure that you are not the kind of American who only comes to look for kids, or have sex or do bad things, because those things happen here, too. Therefore, we pay attention to be sure that you are not that kind of person. Nicaraguans do not have the same level of experience as people do in other places, so they may not be as cynical and maybe a little more naive and trusting than people in other places.
In general, there is no built in prejudice against foreigners at all. In my opinion, there are no specific judgments about what expats are like. Nicaraguans’ perception of Americans is influenced by their experience. Some Nicaraguans will have more worldly experience like living in the United States, while others who have lived in Granada their whole life just take it that Americans come and like it here in Granada because it is cheap and the Americans have a lot of money.