If the first time you were made aware of these "conditions" was a note attached to payment, then Buyer's "conditions" are technically not part of the sale and you have no obligation to meet them. They have the same weight and enforceability as if the Buyer wrote in a payment message that you are required to wear a pink tutu while boxing up the item.
If the Buyer communicated these conditions to you in the back-and-forth of the Make An Offer/Best Offer framework before making the purchase, then they have enforceability. If the conditions were mentioned in eBay messages prior to the sale but not part of the Offer framework, then ""maybe"" they have enforceability depending upon the tea leaves and dice roll of eBay dispute resolution at a given moment in time.
Having said that, let's get to the reality of the list of conditions.
Buyer has pretty much said to you, "This is a serious purchase on my part. I am spending money on this item because for it to be worth the price, it has to be able to meet these conditions. I will be checking the item for these specifics when I receive it, so it better pass these tests when I get it, or else I'm sending it back to you and you're going to give me my money back and eat the shipping both ways."
So they have thrown down the gauntlet.
First issue: if these are essential functions for this item, and you have not already verified that the item can do the functions because "...I am unable, unwilling, and/or unqualified to do some of them...", then you were already taking a big risk listing the item (presumably as used) because on eBay, "Used" almost always means it still works normally. So regardless of to whom it was sold or to where it was sold, if you are not confident that it fully functions, maybe it would have been best to have it professionally tested prior to listing.
Second issue: the reshipper. Yes, eBay rules say items reshipped lose their Buyer protection, but maybe/maybe not if the case goes to eBay for decision, and who knows what PayPal is going to to.
Third issue: agita. Sounds like problem Buyer, not because they have standards, but because they announced their standards after the sale, which IMO is unreasonable and reveals a certain mindset that "does not play well with others."
So IMHO you should do whatever you can within eBay rules to cancel this sale.
Normally, when a Seller cancels an order it will cause a defect to be placed against their account, but the added conditions placed on this transaction by the Buyer after the sale should be enough to allow you to cancel the sale without getting the defect. Call eBay Customer Service and see if you can convince them to agree.
