In its first adjudication, the FRSB rejected a complaint from a man who claimed he had been aggressively targeted over two years with 13 CRUK mail packs containing pens. The board concluded there was not sufficient evidence to show all 13 had been received within the alleged two-year period.
"I wish perhaps there had been a mild rap on the knuckles for CRUK or at least a request to review the way it keeps its database in order," said Lepper.
"Although it is an isolated case, it is a tactic likely to be repeated up and down the country and some people may get very annoyed or feel a bit intimidated."
Lepper has said he was "a bit of a sceptic" when the FRSB was launched last year but is now "a bit of a convert".
Richard Taylor, executive director of fundraising and supporter marketing at CRUK, said: "No one wants to receive large volumes of unsolicited mail. We have to ensure this doesn't happen."
An FRSB spokeswoman said the complainant was satisfied with the decision.