What are these spots?

Sometimes it's actually paint from inside the barrel, sometimes it's dust. Unless it's really a large spot, you probably won't notice it in your images....

 

It's probably some kind of dust. Oil drops seem less likely, but you might want to check the aperture blades for oil; if they are oily I'd return it straight away. AFAIK fungus doesn't show up as isolated spots. If the lens doesn't show haze or fungus I wouldn't worry about the spots, I've had many older lenses with some dust inside and it's inconsequential unless there's something like a layer of dust on one or more elements.

 

It is almost certainly little specks of paint/metal. The seller may well have been truthful, as they can hide in the edges or threads and pop onto the lens when ... kicked about in a postie's bag ... or something.
Don't worry about them UNLESS you see a problem with the images it takes. (They are easily cleaned out of an old manual lens anyway)