How do Lobbyists have Influence, but are Limited? (EX)

-Lobby Firms spend £2 Bil every Year to Influence Decision Making, and Employ 4K -Concerns have been Raised that Influence has been Bought. -However, MPs has Rules Limiting them to Accept Money from Lobbyists that aim for the MP to Agree with Lobbyists Viewpoints - Must be Registered in Electorate Commission