I was told once that Maggs means son of margreat but I dont think that is right
Also I have been told that it comes from the word maggot as in our ancient relatives looked after the apples in orchards in Someset and surrounding counties, making sure they were fit to be sold in the markets.Now whether they owned the orchards or worked for someone else, or even if this is true I dont know.
I hope this leads you on the right path and let me know what you find out.
Richard Arthur Maggs.
Son of Richard John Maggs of Cardiff, son of Arthur Maggs and Joan Maggs of Cardiff