Talk to the owner about his methodology in collecting rent. If he's not following this format, then it would not be uncommon to have that much delinquency.
1) Rent is due on the 1st and late after the 5th
2) Send a demand letter on the 7th
3) File an eviction after the demand letter expires
4) Go to court and get the eviction
5) The date the appeal possibility ends, get the writ of execution
If the seller is following these five steps, then it would definitely be a huge concern that so many tenants are behind. But I doubt he is.
We have cleaned up collections far worse in the past -- parks with 50% uncollected by the middle of the month, for example. You can get a park's collections turned around in about 90 days by enacting a "no pay/no stay" policy. It isn't pretty on the front end, but after you train the tenants that rent comes first, they rarely fall back into the trap, as long as you stick with the five steps shown above.