I currently work for a consulting firm (A), who sell my services to a big client (B) whose office I'm spending my work-time at. Effectively, I'm always at the client office and almost never see the company I'm working for.
Things being as they are, the consultants here are way closer to B than the A-salespeople and hear a lot of things on the client side. I also have a casual relationship with my direct B-manager (on the client side) and we're able to have friendly conversations.
Multiple times, that B-manager slipped in the conversation how much the A-salesperson in charge of us was annoying him and the other B-manager on our floor. The grievances point to the A-salesperson's efficiency not being up to the standards the two B-managers are expecting (things such as: not knowing on the spot the contract's monthly price for a consultant they are trying to place, lack of care in reviewing the invoices that caused small inconsistencies - such as trigrams being wrong).
Not making any judgment on that (since I only heard one side's version and would personnally tend to minimize those mistakes), I'm perplexed as what I should do in such a situation. I'm relatively new in the consulting business (less than a year). I feel like my "loyalty towards my employer" (as is expected and per my contract - working in France) should lead me to share as many useful informations about the client to my A-management, as long as it does not breach any non-disclosure policy. On the other hand, I don't know if it's my place to tell my A-salesperson, and reveal what are in fact off-hand casual conversations.
Moreover, I get really rare opportunities to exchange informally with my A-salesperson (only when they come to the B-office in fact). I would prefer to have this exchange off the record, as a friendly pointer, to avoid any written traces that could backfire in any way (don't know how or why, but again, don't know if it's my place to share that information in the first place).
TLDR: Should I let my salesperson know that their behaviour is causing slight dissatisfaction with our client and that the phenomenon is escalating? If so, is it a problem to do so informally and off the book?