Everyone suspected everyone else, but of what?

Everyone suspected everyone else of being a robber or murderer. From the text:

"In those days, travellers were very shy of being confidential on a short notice, for anybody on the road might be a robber or in league with robbers. As to the latter, when every posting-house and ale-house could produce somebody in "the Captain's" pay, ranging from the landlord to the lowest stable non-descript, it was the likeliest thing upon the cards. So the guard of the Dover mail thought to himself, that Friday night in November, one thousand seven hundred and seventy-five, lumbering up Shooter's Hill, as he stood on his own particular perch behind the mail, beating his feet, and keeping an eye and a hand on the arm-chest before him, where a loaded blunderbuss lay at the top of six or eight loaded horse-pistols, deposited on a substratum of cutlass."