Co-operate as default if you don't have a good read on whether the other person is co-operative is included in my suggestion, is that not enough for it to feel non-aggressive to you? Tit-for-tat, with co-operate first turn. If they come in at you sufficiently rudely without giving a chance for a reasonable request, you can take that as them playing defect preemptively.

And it's not specifically expected reciprocation I'd look for, but whether the person would be as helpful to a person in general if they were on the other side of the situation.