Seller involvement post close

I came across a Reddit post on this and wanted to get some real-world perspectives from folks here. The situation in the post was a retiring seller (80+ along with his wife), where the wife wanted to stay involved part-time after the sale. The top advice there was not to let the seller linger too long, as it can create confusion with customers and employees, and can also undermine the buyer’s ability to take over. There’s also the SBA angle, where seller involvement is typically limited (around 12 months max). That said, I’ve spoken to a few buyers who are actually thinking of keeping the seller involved for longer. I'm in the process of acquiring a small manufacturing business that’s been run by the same owner for ~30 years. So this question is very real for me: How long should you realistically retain the seller post-acquisition? The seller believes the business has strong goodwill and will continue smoothly. But honestly, there’s no perfect way to validate that without actually owning and operating it. One thing I’m considering during due diligence is analyzing customer history, looking at the past 2–3 years of clients, repeat business, and concentration. If there’s a healthy spread and repeat orders, I’d feel more confident that goodwill is embedded in the business and not just tied to the owner. Curious how others have approached this: - How long did you retain the seller? - What worked (or didn’t)? - Any red flags I should watch for?