the 4 known hidden venders

[RabMan]

Are you sure thats not a rescue the vendor as the 4th location? I've killed everything on the dock, boat and house numerous times and no vendor spawns.

There were two emergencies that spawned approximately right where you were pointing though.

[TG_WarMachine]

thats what im thinking as well also don't forget in a past update all hidden vendors were changed from machines to people so the forth is b.s

[SHAD0WEN]

the 4th one seems to be bugged. some of my clan mates can get it to spawn and some can't.

[Taaltos]

Here's three.

[DJTrig]

That 4th one is just the rescue the vendor emergency.