To put this in proper context, this would be like back in the day, when sellers were all up in arms about being made to use PayPal, and not posting items until the money was transferred from PayPal to their bank account because they didn't consider it "paid" until then, and of course it often used to take a few days for transfers to occur back then, as well. Or more recently, sellers refusing to post because eBay / PayPal holds their funds for a 21-day period, until they establish a good track record as a seller.
Don't accept sellers doing this as eBay's fault (I mean, in some ways it is as they do it because they don't trust eBay, and that's at least partly eBay's fault), but ultimately it's 100% down to seller choice.
Just a caveat, while I don't agree with sellers doing this for this reason alone, they may have an extended handling time for this or any other reason, and as long as they post within that handling time, they're technically not doing anything wrong and at least you can avoid sellers with long handling / ETAs - it would be more if they have 2 days handling but wait a week due to the payments issue where you can raise an official complaint.
