If they are rust spots, there are too many of them. The faker may have overdone it a bit.
jar by: peter
Hi Allan, The bottom picture is somewhat blurred, but as far as I can see the foot rim is not Ming. The color is too dark and it seems too wide.
Further, if this were Ming the wucai colors would look different, and the decoration possibly less sparse. Personally I would not buy that, it looks like a fake to me.
BTW, the 17th century jars I know are a bit different in shape.