Hi Phil. Consider all estate agents as S/H car salesmen . Essential is a good lawyer, for that go to the Embassy for advice, or by friendly recomendation.
Do not sign up to anything unless you have been satisfied by your legal adviser that all documentation is correct, and if possible, read up from books specialising on Portuguese property law to benefit yourself, for even the lawyers make errors. If your lawyer has a Doctorate in fiscal law, so much the better. Tread carefully & good luck.