"Transferring part of your debt is standard practice here in Spain and has/is being offered by many builders/developers."
Yes agreed, but is it you believe that they do this out of sympathy for those who have been caught out?
No, they do it because they can make more money out of you by inflating prices, but the purchaser THINKS they have got a good deal.
And your observations on: "Are you hoping that in the first example, everyone will deduct your deposit for the SADM premises and then say, let's help you and base fees, costs, taxes on the 100K and not the 140K?"
"However new, key ready, unlived in properties of this size and style" Obvious and aparent, as you will be aware that the developer's funding is often geared, which prevents them from lowering prices of new premises. Which is why many sell to themselves as individuals or to family, so they can then sell on at a lower figure, unless there is of course a restrictive covenant which prohibits, as is often the case on many developments, including those in UK.