Most all MLS's require "Change Forms" to be signed and dated by the seller. This would include; Price changes, changes in status like active to pending, pending to sold or cancellation forms.
 

MLS NAME FORM
Grand Rapids     Change form ( required for price changes, cancellation of listing ( or expiration)
Lansing Change form (need fully completed, dated and signed)
Midland Midland change form, need completed, dated and signed
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