Sales, who has welcomed how show garden judging has developed in recent years, added: "The main priority to bear in mind is that most exhibitors will be inevitably disappointed and, like football referees, judges will be disagreed with. That is the name of the game and no system can avoid it."
The former National Trust chief gardens adviser said: "When I began judging 30 years ago the procedure was summary, even autocratic, medals being awarded by the whole of RHS council visiting the gardens after lunch having viewed them beforehand alone. The president (Lord Aberconway) proposed a medal - or none - and the council voted. Few members of the council were knowledgeable or even much interested in garden design."
Sales said the system gradually developed over the next 20 years with him as chairman of the preliminary assessors, a group of three or four with knowledge, experience and expertise in gardens, garden design, planting, construction and garden history.
Exhibitors began to write their own briefs so that judging could be as objective as possible against a marking schedule that set out the main criteria weighted by overall marks out of 100.
These assessments would take place the day before judging (Sunday), providing the judging panel on the following day (Monday morning) with detailed comments, a draft set of marks and a tentative award.
For the final judging the assessors would be joined by judges chosen by the RHS and the panel would be chaired by a selected member of the council. There would always be a moderation meeting finally to validate the awards.
The system became the worldwide standard. This year, there will be a new criteria-based points system, on which Sales said he is not up to speed.
Sales said: "Over the many years that I have been involved standards have risen steadily in response to a rigorous system of assessment and judging, followed by carefully-considered feedback for those who are not too arrogant to listen.
"Partly because of television, show gardens have become the stars in terms of popularity and interest - rightly or wrongly. More and more money is spent and sponsors expect a return for their outlay. This applies ever-increasing pressure on designers, exhibitors, assessors and judges. The system is broadly excellent but everyone should accept in advance that not everyone will be satisfied with the outcome.
"Every judge and assessor I have encountered has carried out his or her exacting, time-consuming and exhausting work with the utmost integrity and, unlike exhibitors, for no return other than a fascinating experience. I for one learned a huge amount."