Nuts do go off,but luckily in most cases it's easy to tell by sight if something is still good or not.They tend to stay good for a while though,especially in an airtight container!
Nuts in shell are often salted,especially when they're meant for human consumption.Just check the ingredients,as you should with any food product,and you should be fine
I would definitely avoid buying nuts in shell in bulk,as they will go bad if left too long,but if you keep it to a small amount(1-2 pound or around half to just under 1kg)and store them in an airtight container it should be fine.Sometimes bulk products are good,other times they're not worth it and will go bad before they're even mostly used
