I always either leave positive feedback, or no feedback at all. The reason for this is to have 100% positive feedback to sellers so that if I make an offer on a coin, it's more likely to be accepted than if I look like a potentially awkward customer. That said, I've sometimes had good reason to leave a negative. In this case, I'd just contact the seller, who may just be ignorant of coin etiquette, and remind them of the need to treat coins with respect, use paper envelopes for all of them, and most definitely avoid sellotaping the coin itself.