Tax liability on sale of primary residence - 8 plex

[Carter Still]

I am purchasing an 8 plex from a seller who has lived in the building for 18 years. He will profit nearly $500K from the sale, and his biggest Hang up is taxes. 

I’d rather buy the property clean with one payment vs getting creative. Certainly don’t plan on guaranteeing this person my tax advice is correct, but wondering if the homestead rule applies here? (No tax on profits from sale of primary up to $250K for single/$500K if married). 

this question seems dumb if it were a large complex, but seems reasonable on an 8 plex. Please no 1031 advice - this seller wants to retire from landlording. Thanks In advance!