Soak your product in some IPA or methanol. Use anhydrous, or nearly so, alcohol. If its salt, it will not dissolve. If there is any meth there, it will. Filter out the solids. Evap the alcohol and see if you have anything there.
A mix of salt and meth will still vaporize meth when heated. The salt may pop and jump, but the meth will smoke. If there is no meth, there is no reason to put the salt in the reaction fluid.