I work in an industry that uses ALOT of stainless steel. It is a myth that because a product is made from Stainless Steeel it will not rust. There are so many differnent types of stainless steel. The difference is the percentage of the different metals .. I could go on and on defining at lenght all the different types. The most common component that keeps stainless steel from rusting is a high percentage of nickel content. The many many types that are avaiable all get to be called "stainless steel". The high nickel content in stainless will not be able to be picked up by a magnet.... but due to the rising costs of nickel ... some are using other metals with the nickel and the steel to reduce the cost. But one thing is for sure cheap stainless will have a magnet adhere, ie more steel than other more $$$ metals that do not rust.
Most pin manufactures do not list the type of stainless. If you find one that does look for type 304 or 316 stainless, these have very high nickel contents and will not rust . Or find pins made from Nickel.