In the late 1960s I read a fascinating science fiction novella - part of a double header paperback series (Ace Doubles books?) - which I have been trying to identify.
The lead male character discovers he can enter rooms etc where he is ignored - treated effectively as invisible. Room occupants give him a cursory look then just ignore him. He can appropriate money - from banks, take food and possessions without suspicion. Eventually he walks unnoticed onto a space ship and continues the adventure on other planets.
Definitely not Niven’s novel A Gift from Earth. The action as I remember starts on Earth in the not-too-distant future. Space travel is relatively new. The crime aspect I recall alludes to Silverberg, but he does not have his character sneaking onto a space ship on Earth bound for the planets, which is a strong memory for me.