By not being the answer to every question during diligence. A management layer that has been in place for a year, documented processes, and customer relationships held by someone else are the proof buyers accept.
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Owner dependence is the most common reason a good manufacturing company gets a mediocre offer. The practical markers buyers look for are specific: who quotes, who schedules, who handles the top customer, who the plant calls when something breaks, and whether any of those answers is the owner. The fix takes twelve to twenty-four months and is mostly delegation with documentation: getting estimating logic into a costed system, introducing a second contact at each major account, writing down the tribal knowledge around setups and processes, and then actually stepping back far enough that the business demonstrates it works. An owner who can take three consecutive weeks off without the company noticing has proof no presentation can substitute for.