Do us a favour?

Here in London, and I assume most other places, each referee gives out cards to the captains of the teams we officiate. The idea is that we are then scored on our performance and if there is a problem, or we are doing well, we can be independently assessed by the Society. Our grading are then changed up or down. The cards take 2 minutes to fill in and I even provide a stamp.
I try to get feed back from captains in the bar post-match but the card gives them a voice for what they aren’t prepared to say to my face. I hope they will be honest with both the card and over a beer.
There are a couple of problems, the first is the percentage that get posted back; this season only one match has seen both cards returned. I give up my afternoon to do something I enjoy, all it costs the team is my petrol money and beer or two and they get an afternoon of rugby. How much effort is it to fill in the form and post it back or hand it to me in the bar? Less time that it take the barman to pour the first round.
My second gripe is teams that have been on my wrong side all afternoon marking me down out of spite. They weren’t honest with themselves on the field, they can’t be honest with me on the cards. Having been around the circuit a couple of years, it is clear that one club in particular seems to consistently score me lower than my average. They are also a side that are ‘challenging’ to manage on the field. It’s a shame because the facilities and organisation are first rate, but clearly the ‘esprit de sport’ is flat, something you would hope wasn’t a function of the leading public school that feeds the club. LondonRef Jnr won’t be learning the game there despite the convenient location.