Nad, I leave in stand by. Sub amp, I leave on. Dacs, I leave on most of the time, Modi, SMSL Su9. The other SU9 I turn off. I have it connected to the theater.
My preamp and theater amp, I leave on.
I turn headphone amps and preamps off. (tubes). I don’t want the kids to touch them.

If you don’t trust your salesperson, then change salesman or leave. Is he giving you what you need or what he sells. It looks like you’re doing your own research. That is good. Buy what you like from your rep. Then buy your other items from somewhere else. If you don’t love the sound, try the stuff your original rep suggested.
I am about 120 miles from a big box audio retailer. And they do not have their stuff in stock. I don’t like buying and returning audio equipment. What other choice do you have?