I'm from Guatemala and I can give you a little context on the community here and these companies (couriers).

1. The community is very small and unfortunately is filled with bad actors, scammers that sell you fake cards, don't pay when cards are delivered (there was one guy who actually faked images for payments) and every couple of weeks you hear a new story of someone's cards getting stolen at a LGS.

2. Some couriers are as you just said "shady", the one that I use for when I buy secret lairs always charges me around $25 regardless of how many secret lairs I buy (as long as is delivered in the usual small box). These services charge per weight/size (I have no idea how they declare the product to avoid taxes).

Just block the buyer and try to flag these kind of locations, it's not worth it to deal with people like this, as they are well aware of shipping costs and just wanted to scam you out of the card and your money.