Points to consider before buying a previous grow house

[Balkrishna Agrawal]

Question regarding buying an investment property in CA which was used as a grow house in past

Known things so far 

- Growing was done in one room of the house, seller claims it has been cleaned up completely. I would like to know what all qualifies as completely clean here

- Electrical wiring is normal and no unlicensed modifications 

- Structural inspection is also clean.

Seller is ready to discount the price by ~20% from market plus the cost to repaint the whole house 

What are other questions to ask and things to consider in this scenario?