You have to trust the vendor's interest in making a profit. Nothing wrong with that :-)

Closed source (usually) gives you Ts&Cs, support model and some level of guarantee of fitness for purpose which is why we pay to use it. This is not to say that there aren't bugs that seem to take forever to fix, but usually that is not the case at least not when there is a risk of the product becoming unsalable.

Of course there are closed source software or appliances that just are not worth their cost because they fail to mitigate the risks of having us trust what we cannot see, but these usually fail to gain any significant market share.

In these days wit SuperFishes and Lenovos selling out their customers for a few bucks more, trusting that the vendor have an interest in making a profit might not by itself be ok.

>You have to trust the vendor's interest in making a profit. Nothing wrong with that :-)

Sometimes there are conflicts of interest. We have documented cases of 3-letter agencies paying companies to leave bugs or unsafe options in code. Sometimes the backdoors may be more valuable than the product itself.

I suspect many corporate clients found out these days that their SSL MITM software they used made their infrastructure vulnerable.

This is very true. However trusting that open source does not include such vulnerabilities is a leap of faith we cannot make which is why auditing and quality control process are needed.