With a price disparity of the magnitude that I have illustrated, the simple truth is that people are going to go for the cheaper option and buy direct from Germany. In the present climate, personal finances are being hammered from all directions and that means passing some of the pain on to others.In fairness it's not a level playing field. The German ebay supplier often has this as a sideline to his main domestic business as I was illustrating above, or doesn't have any other business having costs of maintenance.
The UK supplier here is solely dependent on their e-bike related sales to support them, their premises and their after sales service year round.
Delivering very low prices for anything via ebay is easy.
If the differential was £50 I'd buy in the UK, but £150 is too much. I know where this is all heading in the long term and it's rather frightening.