Hi, welcome OP. I'm not an expert but I'm interested in similar problems and maybe can offer my current practical understanding. Some of this may be things you already learned about, so I'm sorry in advance if I'm rehashing stuff you already know.
I don't know what you're learning in school about ethical relativism, but in terms of the questions you are posing in your post, I think the specific field of study you are looking for is normative ethics -- what should be the standards or norms of ethical behavior that we should set? Within this field, there are three major approaches --
virtue ethics,
deontology, and
consequentialism. I don't think any of them are all that convincing on their own necessarily, but I think some kind of practical amalgam of the three can be a good foundation for ethical behavior. Given your methodist background I would guess you are probably most deeply rooted in deontology, so checking out some ideas like Kant's categorical imperative might be a fruitful place for you if you are looking to philosophy to continue developing your ethical perspective.
Let's take for example the first thought experiment you posed:
Lostlittleboy wrote: ↑December 22nd, 2018, 6:42 pm
If morals are relative, is it OK to hustle people out of their money? Does it matter that you are taking advantage of someone? The only loss is that they are either ignorant or you'll never see them again. I was raised democrat and Methodist so I kind of carry a lot of those teachings with me, but if not everyone follows suit you are kinda stuck being nice while others just don't care.
So here's a really shallow take on these three schools of thoughts regarding hustling someone out of their money:
Virtue ethics would say no, it is not ethical because you are behaving in a dishonest and uncharitable way. Don't hustle people because what kind of person would that make you be? Not a virtuous one.
Deontology would say that we have a moral duty to behave in the way that would be best if everyone also behaved that way. Deontology according to Kant posits that humans are ends, not means, so hustling someone would be immoral because it breaks our moral code, which hopefully includes "Do unto others as we would have them do unto us".
Consequentialism allows for more gray area. Hustling someone would be immoral if you get into the habit of hustling people, and soon nobody trusts you and the end result there is a bad consequence for you. But let's say you were hustling someone because you've hit a rough patch and need to provide for your family in a pinch -- a consequentialist might say that it's not a bad thing to do -- if you can get away with it. Do what you gotta do.
I have my own thought experiments that might shed some light for you --
One is the Iterated
prisoner's dilemma. Basically, it's a game where you can cooperate to get a mutual beneficial payoff, but if one person defects, they can get a bigger payoff and the other person gets nothing -- but if both people try to screw the other, everyone gets nothing. In this game, if you screw people over too many times, people figure out that you're not trustworthy and you get ostracized and screwed over in return like you deserve. The most effective strategies that have come out of these AI tournaments are pretty interesting: tit for tat is probably the simplest strategy that can work consistently (screw people over only if they screw you over first), collusion works really well also (screw over everyone not in your preselected group), and payoff control -- which in the simplest case means cooperate and give people chances until they screw you over past some threshhold that you've calculated that you can't tolerate -- after that you screw them over no matter what they do.
One insight that comes from biology is called multi-level selection theory. This idea currently underpins my thoughts on ethical behavior. It goes like this -- selfish individuals win out over altruistic individuals, but groups of altruistic individuals will win out over groups of selfish individuals. So I have been using as a practical model my ethical behavior by protecting myself from selfish people when they can actually do me real harm, but being as kind as possible to altruistic people -- within my means. It does nobody any good if you become a burden. But if you are well-positioned to handle it, tolerating selfish behavior might give you a bigger payoff in the long run as well -- you might be able to convert selfish individuals to cooperate with you, and enlarge your altruistic group and thus increase your power in that way.
I definitely sympathize with the complaint that it seems like if not everyone follows suit you get screwed. Having a conscience and feeling guilty can seem like a dumb idea sometimes for sure. I'm coincidentally working on a similar problem on a set of ideas posed by Gandhi as the Seven Blunders of the World in
this thread, although I don't think I'm necessarily doing a great job of it. I imagine that I definitely come across as a bit of a jerk, but you might be interested in that topic since the first blunder, Wealth Without Work, seems to be something you are referring to directly in one of your thought experiments later on.
Beyond that, you might find some useful criticisms on moral relativism to raise with your professor at
this link here (ctrl f for criticism). It takes the perspective of cultural anthropology and challenges moral relativism on the basis of cultures that support things like generalized intolerance or female genital mutilation etc.