Find out how much the borrower put down

In a word - no.

I can only think of one platform where the loan investment proposition may contain this information but generally my impression since being involved with P2P lending are the background details regarding the loan ‘opportunity’ have gradually been slimmed down. Many platforms over time have tried to force feed investors the impression that it's all to do with the asset. The borrower, especially their background is immaterial.

As platforms seem to be having more difficulty in filling loans then this may change although personally I do not feel it is in their DNA to do so.

You could always ask them direct. Whether you receive an answer or one you can rely on is debatable.

When it happens, Lendy has mentioned it. For example DFL018: "The borrower will be injecting a total of £600,000 towards the total build costs of £1,810,000."

There was another DFL where the updates stated something along the lines of 'the borrower continues to fund the build costs themselves' but I can't remember which loan that is / was.

I wouldn't say it was the valuer's job to identify surprises beforehand.  I'd say their job was to identify the middle ground. What normally has been the case and will therefor likely be the case in the near future.

If a particular valuation is badly miscalculated, proving it isn't simply a case of say 'You said it was worth £2 million, but it only sold for £1 million.'  Proving it is having several independent assessors look at the data available at the time and see whether the wrong data was used or whether method was applied incorrectly.

As for skin in the game, the idea of every investor is to minimise their risk. Developers are investors and they are entitled to minimise their risk, by using as little of their capital as possible.

While this is true it would be sensible for the platform or us as investors to determine what exactly the borrower will lose if the loan goes into recovery before putting our money into it.

That said I think there is a very good case for platform credibility to take on risk and invest a significant proportion of their loan origination fee into the loan itself on the same terms as the rest of investors or even on a first loss basis (via say a wholly owned subsidiary company if that would keep the FCA happy). It might not be in the platform's best short term interest but I think that aligning goals with investors would see a definite improvement in decision making (e.g. not selling well secured loans at a discount, making more careful assesments of credit risk when originating new loans, investment in improving recovery effectiveness). Personally I would be a lot more confident in loans where the platform has a solid financial incentive to see loans repaid in full

Currently if a borrower stands to lose nothing and the platform makes most of its money risk free from origination fees and rolled up interest then lenders are more likely to be encouraged to take on rubbish loans on which they will lose money. A platform where investors lose money does not have a long term furture.