When I receive payment for chips, I rarely if ever take more than 24 hours to ship them out, or 48 if the payment occurs on a Saturday afternoon. I let buyers know immediately if there is any (rare) holdup, and always send tracking info from the parking lot of the post office, so I don’t forget.
The one time I had a foreign shipment disappear, I sent the buyer another batch of the same chips, with the understanding that he’d send one set back if the missing one arrived. (It never did.) They weren’t cheap chips, but I felt that was the right thing to do.
So I can’t see any excuse for this happening to a high percentage of one seller’s shipments. There shouldn’t have to be anything worked out or any patience needed from buyers. Either this seller is corrupt, or incompetent, or both.
RE: Negative feedback: I have never sent it, though there were a few times I should have (e.g. due to extremely sloppy packaging which led to damaged chips). The reason is the same others have cited, and just generally not wanting to sow ill will.
Maybe a different system is in order, where feedback is more anonymous. Someone who feels wronged by a bad review could appeal it to a mod, with neither party knowing. It also might be useful to have a sliding scale (Excellent/ Good/ Average/ Below Average/ Unacceptable) so people feel more comfortable giving less than perfect reviews.