Yeah I guess that makes sense for some people. I'm just not in a financial position where I'd let an AI buy a $600 used guitar without me taking a look at it first.
If I were going to automate something like this, I'd have a suite of products to watch for - common enough to be reasonably frequent but obscure enough to be mispriced, kinda the whole idea behind secondhand ocmmission / antique / estate sale shops.
I don't know how EBay is supposed to differentiate automation from real users in this scenario. To get around it, all you need is human intervention at the last act, so you could fire up your bot and have it forward the "buy now" link when all parameters are met? Maybe they just don't want AI companies to have an argument for some sort of revenue sharing or commissions.
On the other hand, when people list a steeply discounted item, there's usually a good reason why they do so - opportunities for easy arbitrage are rare because people would usually prefer not to give you free money if they can help it. Signing up to automatically buy broken items for $600 without so much as looking at their condition seems like an easy way to lose a lot of money.