Agreed. I mainly do that with smaller sellers though. I don’t mean to generalise, but I find the high volume people will just give you some kind of automated response when you contact them.
There was a case where I bought $300 worth of blister packs(ebay seller that was local) and the guy showed up with a box full of NM/M top loaded holos and asked me $100 CAD for it. There was well over 100 cards in the box, including a Gold Star Mew and a couple Shinings, Mint Base Zard,etc… I was going to maybe maybe $100 profit on the blisters, but that little box earned me so much and I still have leftover cards I think I will just donate to kids. 
There’s even a collector here that managed to get his hands on a Pikachu Illustrator card and other very rare items, as they contacted an ebay seller they bought from.
www.elitefourum.com/t/shyguys-collection/17989/15
Edit: It’s actually the seller that contacted them, but it still goes to show having the right contacts at the right time is key. I’m actually surprised with some of my ebay experiences where buyers or sellers don’t respond to messages and they could have either earned another sale or a good deal on a future purchase. Oh well… Too bad for them.