[WorldMaker]

My understanding is that wire transfers are guaranteed by the nation state at the receiving side, which is one reason most Nigerian scams are Nigerian because Nigeria will almost never refund/reverse a wire transfer and other countries have different laws/perspectives.

I believe Cashier's Checks are still the safest option, because of most Cashiers require upfront escrow of the funds involved. So long as you trust the Cashier bank in the middle of the transaction, you should be safe?

> Are PayPal funds guaranteed?

Nope. Lots of eBay scams in the history books.

> Is receiving something like Bitcoin/Ether the only way to guarantee funds are real?

Depends on your opinion of forks, the likelihood of 51% attacks, and even the underlying assumption that cryptocurrencies are "real". Not to mention you probably aren't using a cryptocurrency as your day-to-day currency so you'll encounter plenty of scams in the edges and exchange markets.

Also, there have been Ethereum smart contract scams already.