I recently attended a discussion about how Native Americans followed a Sacred Economy model in which they didn't price items, exploit nature, and how they shared everything communally, with no concept of private property--how legit is this?

I recently wrote a graduate paper for my Indigenous Governance class on Native American/Indigenous/FN women and the roles they play in their communities, I looked at IG/FN womens roles in the environment, economy and governance. These three areas are based on a core ideology (although it should be noted this is a broad statement, not a specific one for every single community) that the relationship with the land is based on reciprocity (giving and sharing). Humans are seen in the cosmological stories of FN/IG (again most not all) as being younger and coming to existence after the plants and animals, as such the responsibility is on humans to care for and pay gratitude to the plants and animals, and also show reciprocity, that sharing is caring essentially. Taking more than is needed, taking only for yourself and not sharing etc is largely not a part of the larger cultural ideology. A quote from my paper: "In these creation stories humans arrived last onto Turtle Island and as such were responsible for the well being of the plants and animals that existed before the arrival of humans (Watts 2013). This respect is extended to the soil and land for which humans are understood to come from made possible by the female cosmological figure, further embodying people, plants, and animals to the feminine (Watts 2013). As a result, the relationship between the feminine and the human and nonhuman aspects of Turtle Island have been embodied over generations and engrained in the clan systems, ethics, governance, and ceremonies of many Indigenous communities (Watts 2013)." Watts sourc: Watts, V. (2013). Indigenous place-thought & agency amongst humans and non-humans (First
Woman and Sky Woman go on a European world tour!). Decolonization: Indigeneity, Education & Society, (2)1, pp. 20-34. So that last part, how the idea that humans need to care for and respect their elder plants and animals and how it has been engrained into their societal structures is really key. The reciprocity idea is from the top down, governance, economies, clan systems are all based around this idea of reciprocity and caring for the land. You can then see how many communities then have a deeper respect and understanding of the balance of them and the land and animals. Another paper (Baker, J. M. (2020). Do Berries Listen? Berries as Indicators, Ancestors, and Agents in Canada's Oil Sands Region, Ethnos, DOI:10.1080/00141844.2020.1765829 pp.1-22) goes into specific detail of berry picking and the importance of caring for the land and how that impacts the berries and their ability to live on the land, but also the very human connection to the berries, berries in this community are seen as hearing and knowing, and the success to healthy and bountiful berry harvests and bushes is through reciprocity (sharing with the community), positive thoughts and environment (picking as a group, sharing happy stories and generally thinking happy thoughts as the berries are understood to 'listen.') but also the connection to the land which is severed due to O&G development which impacts how the berries thrive and in turn how the people thrive on the land itself.
One of the roles that came up a few times in my research was the role of women in the gift giving and reciprocity events and ceremonies, which is a part of some communities economies. Gift giving in the communities I was looking at (Canadian FN/Indigenous mostly) performed various types of gift giving as a way to share the foods/resources/wealth of the community with the elderly, sick, and those who were unable to collect food and resources, essentially the vulnerable populations within the community. These are the sources I used for my paper that spoke to the gift giving ceremonies (or gratitude ceremonies as they can be called):

Kuokkanen, R. (2011a). Indigenous Economies, Theories of Subsistence, and Women: Exploring the Social Economy Model for Indigenous Governance. The American Indian Quarterly,(35)2, pp. 215-240; Wolfstone, I. F. (2019). Sharing Economies and Indigenous Matricultures in the Land Now Called Canada. Canadian Woman Studies. (34)1&2, pp 13-18. My paper also discussed IG womens role in their collective economy, I highly suggest looking at Rauna Kuokkanen, she has written extensively on the role of IG women and the economy, and also details some of the ideologies and values that are seen across many IG communities. It does need to be caveated that not all IG/FN communities are alike, they may have some overlapping values and ways of living, but many do have different economies, can be lead more by men or women depending on the community etc. So you can't place a blanket statement that all of them were thinking the same. But it is a common theme. A direct quote from my paper sums up the thoughts of literature and accounts of IG/FN communities and the economies some of them lead: "Indigenous economies are reliant on the stable and continuous relationship between humans and nonhuman beings, which are directly linked to the value of reciprocity embodied through many of the cultural, social, and spiritual practices in Indigenous communities (Kuokkanen 2011a). The practice of harvesting and other land-based activities through subsistence practices establish these connections, and provides important social, cultural, and economic contributions to their communities (Dalseg 2018)." Dalseg source: Dalseg, S.K., Kuokkanen, R., Mills, S., & Simmons, D. (2018). Gendered Environmental Assessments in the Canadian North: Marginalization of Indigenous Women and Traditional Economies. The Northern Review (47), pp.135–166