1. Found out you used their knives to go murdering
2. Sells knives in a fashion where it's possible for them to prevent you from buying their knives (i.e. direct to consumer sales)
Would almost certainly not "be more than happy to continue to sell to you". Even if we ignore the fact that most people are simply against assisting in murders (which by itself is a sufficient justification in most companies), the bad PR (see the "found out" and "direct to consumer" part) would make you a hugely unprofitable customer.
> the bad PR (see the "found out" and "direct to consumer" part) would make you a hugely unprofitable customer.
That... Doesn't happen.
Boycotts by people who weren't going to buy your product anyway are immaterial to business. The inevitable lawsuits are costly, but are generally thought of as good publicity, because they keep the business name in the news.
People who buy (and make) firearms are... pretty close to the exact opposite.
There will always be some company willing to sell to even the worst person, in any product category.
The response that companies have to boycotts, and the results of the boycotts themselves, are fractally chaotic at best.
But even most nominally socially-aware companies are reactive, rather than proactive.
