Hello Frilly,
On Scotlandspeople you will only get a result if the information you put in to their search engine is exactly as is on the marriage for Thomas, and Mary, ie the spelling of Thomas, surname on his wedding to Mary, is McKeon.
So to find the marriage put McKeon, in the male surname box, then Thomas, in the forename box, then in the female surname box put Starkey, then Mary, in the forename box, year range 1869. there is only one hit thats them.
Regards
Jonn.