Where one person's name is spelled in different ways in different records, this can be a difficult genealogical problem. County Clerks, the ensign in a military Company and other records-writers in the 18th century and early 19th century spelled items as they heard them, and the handwriting of some was also an issue.
One approach would be to carefully establish the person's life-path. This means collecting every single original record you can find. Was there a series of military rosters that clearly listed one person under different spellings (say, more than one giving the same enlistment date or other information that must have belonged to one person)? Were there deeds relating to one clearly-defined property (with name of tract, or giving the same ownership history or giving identical metes-and-bounds descriptions) that spelled a name in different ways? What about tax assessment lists and court records regarding individual cases?
Only the most careful and thorough acquisition of records has a chance of establishing an identity.
I am sympathetic to the Sears/Sayers (not to mention Saires, Sares, etc.) issue, since one of my distant cousins married a Sears/Sayers whose surname seemed to be spelled a little differently in every record.