We bought from Zapata builder at El Raso, outside Guardamar. We told our agent, Millennium, who were doing our conveyancing in their legal dept (don't get me started on that one, I'll be here till new year !) that we did NOT want to underdeclare & they fobbed us off with "it is YOUR choice & NOT the builders" !!!
When we were sent the papers detailing monies & cheques we needed to ensure were ready for day at notary we saw that the builder wanted a certain amount in "black money" & a cheque for the rest (We bought for 195,000 euros of which 146,250 euros was declared) We obviously complained but just were told "it's like this here, THIS is the way the builders work". The builder wouldn't complete otherwise & he had lots of our money. We HAD to comply or lose our money & no one is going to do THAT. We were told to bring our contract to the notary & the builder took it from us (we HAD made a copy) & gave us same but with 146,250 euros on, rather than 195,000 euros.
You MAY say we should have had a totally independant solicitor & I fully agree but everyone tends to get sucked in by these smarmy talking agents who love you till they get your signature on that contract then proceed to turn your world upside down. Anyway it wouldn't have done much good in getting the builder to declare fully as we have our own website for El Raso & those who have bought from Zapata all say the same regarding his underdeclaring.He just won't & he ignores you till you give up.
I wish you well.