The middle stamp is supposedly a 2 (dos) reales error in the colour of the 6 reales - instead of the red it should be.
Edifil specialized does list a 2 reales error in blue (Edifil 8ec), with CV of of 490,000€, and 760,000€ for a pair with the 6 reales. The single or pair would be the highlight of a Spanish auction (e.g. Soler y Llach) in the event it came on the market.
You'd have to be crazy to think that a random
ebay seller would both somehow have & and be selling an entire block of 9 for 3,500€, or even that such a thing exists.
~Greg