Duke has a long history of shady dealings. I'm not nearly as plugged into the recruiting game as I was a decade ago, but there were a lot of stories I heard back in the day. No idea if they're still dirty but they certainly have been at times during the K era.
The interesting thing is that from most of the stories I heard back in the day, buying players doesn't seem to go down the way most fans assume. It's usually not bags of money... Most of the coaches have a level or two of separation from the guys who are delivering the benefits... plausible deniability... sometimes it's as simple as giving a set of select boosters a list of players they want, and having the boosters figure out how to entice them. The coaches who are good at it rarely know any of the specifics.
IMO Coach K has gotten a lot of mileage from the 'Vitale shield'... Dickie V was always adamant and very vocal about how K 'does things the right way' and I think a lot of people have run with that over the years and just believed what he said. It's amazing how much of an influencer Dickie V was in the 80s and 90s, and even into the early 2000s.
(Also, FWIW the only coaches I ever heard singled out as '100% never cheating' in the recruiting game were Bob Knight and Mark Few).