Why or how do you trust home security (camera) setups?

There's plenty of DIY options out there that seem to provide the same quality and given everything we know about privacy and security on and of smartphones, I was wondering how people trust home security companies?

DIY is, of course, a matter of setup and maintenance time but I went into a shop that specializes in home security and the sales men made a very bad impression on me.

Any recommendations and maybe even proof that these companies are trustworthy, like open source software, that trustworthy friends, most of who don't believe in any other home security than big dogs, can check?