Welcome.
Get used to it. The feedback the person left you is just an opinion and I would still trade with you if the circumstances are right. The feedback is without a reference which makes it pretty useless for those that care to read what it was all about. That red -6 might scare people away, true. On the other hand refusing escrow or any other form of security for the other party screams scam. A new account is easy to get, it will get easier once your account is more established.
Obviously, I'm facetious. But seriously. I don't feel like I deserve half the slack I've received since getting here, but hey! That's the internet!
Not only is this the Internet, but consider this the Internet of the 90's. The attitude towards trusting others is pretty similar.
I doubt you will, but you are welcome to try.
There are different kinds of escrow. E.g. multi-sig or ricardian contracts[1]. Yes they also require a 3rd party, but you do not have to full trust said 3rd party.
TL;DR: Ruling out escrow services, what are some safe ways to trade items for Bitcoin? How often to do you use them? And considering my company did adapt an escrow service for our business, which one would you personally choose and why?
Since you are dealing in high value items its probably best to invest some time into multi signature escrow. There are plenty reputable people here. If you do not want to use escrow what could you offer to make your customer feel safe? After all (just some perspective) you are basically asking someone to give >400$ in cash to an anonymous stranger with a mask on that promisses to give you some hardware. Well you are not even physically close to the other person so its even worse.
[1] https://github.com/OpenBazaar/OpenBazaar/wiki/Contracts-and-Listings