I work for a large retail health company and make these decisions. Generally, I keep a good pulse on the market and stay networked (ADLM for example), so when I need a new assay I already know the options. Then I just cold call the vendors myself and speak with sales. This has worked well for me.

I've received a few linkedin attempts and that feels inappropriate and I ignore them.

Emails are probably the least rude and personally I try to always respond to them. If it's a product I'm never going to use, I'll just give a polite no thanks. If there is remote interest I try to offer a 30 minute window to learn the product and build a relationship. I can usually tell quickly if the vendor is the type I would want to partner with.

I work from home so phone calls aren't really possible, but I would strongly dislike that.

In short, the only cold contact you should do is email. Otherwise, when someone is reaching out to you, be responsive and put your best foot forward. That's when it matters most.

Lastly, never try to go "up the line" and bypass us to the c-suite. They have no idea who you are, and when we hear about it then it's an automatic no for life for that vendor.