Contractor insurance - rely on 'company' or the sub?

[Kelly G.]

I am having replacement windows installed in my rental SFH (WI); (didn't know where else to post this). The window 'dealer' (Zen windows) has liability insurance; they use sub-contractors for installation. I asked for proof of insurance from their sub-contractor a few days ago and . . . silence. I'm hesitant to move forward w/ this dealer, w/o adequate liability and worker's comp insurance (if appropriate) from the guy(s) actually doing the work. Or is the 'dealer' liability sufficient? Have not dealt with a 'dealer' and sub-contractor before. No local/state licensing/permits required. thoughts??

thanks

Kelly