Did your friend grow a couple plants that turned out decent and is now considering himself a Master Cannabis Gardener and with the best strains he'll be the king?
If so it doesn't matter. Anyone can grow good weed.
Many people don't want the "Best" strain that will leave them dazed and confused. Some people want lower THC strains. Some people want high CBD strains. Some people want edibles.
Then there are the regulations and up front costs. Does your friend have sufficient funds? It's going to take a five figure amount minimum to even get started and have any chance of success. There are regulations, licensing fee's, etc. You can't just move to a legal state, start growing the "Best" weed, and have it sold through the dispensaries, and then just start counting the cash. The dispensaries have all the suppliers they need. This is now a business and the people involved are business savvy. They are not some closet grower that thinks they can grow good weed.
Tell your friend to start looking into the actual requirements of getting involved in the marijuana industry. It's not a game.
Here are the FAQ's for Oregon. Other states will differ. But this should be a starting point. What strains are best doesn't matter until you get all the legalities in order.
Q: How much are the licensing fees?
A: A non-refundable application fee of $250 is required for all license types.
-Producers:
-Micro Tier I: $1,000
-Micro Tier II: $2,000
-Tier I: $3,750
-Tier II: $5,750
-Processors: $4,750
-Wholesalers: $4,750
-Retailers: $4,750
-Micro Wholesaler: $1,000
-Laboratories: $4,750
-Sampling Laboratory: $2,250
http://www.oregon.gov/olcc/marijuana/Documents/MJ_FAQS.pdf
These are yearly fee's.