As a general rule, in Portugal, offers are not "a thing"...
We've done a lot of serious pre-buying, and have bought 4 times in Portugal. All were Portuguese sellers:
1 - apartment in Lisbon suburb, high demand, reasonable price, seller moved by 1.5%;
2 - ruin in rural central Portugal, no demand (in this specific area), reasonable price, seller moved by 9%;
3 - house in Santarém, moderate demand, relatively top end price for what it was, zero movement, and mild offence at the suggestion;
4 - uninhabitable apartment without habitation license, over the top asking price, zero movement, became very difficult at the suggestion of an offer.
When we have sold, again always to Portuguese people, we've been offered the asking price without offers.
In discussion with many agents, in conjunction with our experience, I would say that you should not assume that a Portuguese seller will reduce by much if anything, and they may not understand or even be mildly offended. If you're buying from non-Portuguese people, or in areas where non-Portuguese buyers are common, you may have more success.
Naturally, a good agent would have some insight into the likelihood of an offer being accepted.
By the way, some of the hassles can related to inheritance properties, where several relatives share the inheritance, and disagree with the price, or even with the sale... This is rarely a "thing" in Canada, the UK, etc.