[note reply-to] Hi,
What kinds of guarantees are there that if someone buys it, that they will actually be able to get and keep this Class B?
An Internet address is just a 32 bit number that has uniqueness guaranteed by the registries. That guarantee holds regardless of who is actually "in possesion of" the address. If an organization with a surplus /16 agrees to let another organization use that /16 in exchange for compensation of some sort, that address will still be routable on the Internet if it was routable before the exchange. Of course, whether it is actually routed is another story. Given the registries do not allow for outright transfers of this sort directly (see RFC 2050), one course of action would be for the original "owner" to sell the "right of use" of the /16. Of course, the appropriate action (according to RFC 2050 and historical Internet culture) would be for the original "owner" to return address space they don't need... Regards, -drc