I just feel like it would be cool to have a standard for trading so that newbies or experienced people don't rip people off or you aren't given the extraordinary prices for otherwise easy things
how I would set up a rating system as far as mineral worth
coal->redstone->iron->lapis->gold->diamond->emerald (it is much rarer, and I know you can rip of villagers but a lot of factors can happen to them)
here are my baseline for some common and needed things for people
1.cobble stack-->1 iron ingut
2.horse (white)-->4 iron blocks and 2 diamonds
3.horse (other colors)-->3 iron blocks and 2 diamonds
4. diamond->9 iron->5 gold->2 emeralds
5.stack of wood/planks-->3 gold-->1emerald
every price can be changed but I thought that it would be a good baseline