What kinds of business tend to have gross profit which is over 80% of revenue?

Non legal ones

I afraid there is no suitable specific answer for your question if you
wanna learn about legal opportunies, you asked generally I think.
 
You need to think about several different efects such as resources,
the taxes, budget, salaries if you gonna have employees etc...By the
way in every country the tax is different and budgets also salaries
and due to several facts the rents or gas priceses will be different
this means that the profit will differ easily according to the
geography.We can have alot of examples.
 
Mine and Petroleum companies have the biggest profits over all because
there are a few companies related allover the world and they are
powerfull and they nearly don't pay any tax to none of the
countries.They are very close with the investment and banking too.

Over all ...  frde-ga is the best and only answer to your question.if
you dont pay any tax and can be able to rule the standarts for your
company all over the world (you need to be very powerful to do that)
you have incredible profit.But this is illegal as you see.
 frde-ga is right sad but true.

Retail sales of popcorn and helium filled balloons are well over 90%.

-=clouseau=-

"Gross profit" is what's left over after "cost of goods sold", which
may excluding selling expenses, and does exclude overhead, so
Clouseau's examples and others may meet that definition of "over 80%
of revenue".

Prostitution is not illegal everywhere, and could be high on the list.

Real Estate (Buy and Sell Homes )