LondonElite continues with consistent and appalling advice with 'The wider point is that, within/among European, no IDPs are necessary.'
Why are you insistent on giving this advice and your complete lack of understanding of the simple points being made?
'I also don't know what rental agency people should or should not enforce' - quite right, you do not. No rental agency is obliged to check on your failure to be legally carrying an IDP.'
Give it up, stop suggesting people should break a country's law.