the Dutch seem to be pretty straightforward and co-operative guys, as my experience with them shows (also at Marktplaats, several times), dealing with them has proven to be safe. also, in most cases they accept offers - be real, though, when doing so as they don't like bargain seekers. and a Best Offer is a Best Offer, hence no, if the offered price is okay the seller won't wait until the listing ends, just as at eBay.
moreover, the Dutch look not to really prefer PP - all of my purchases have been via BT. so the only thing you can rely on is the listing, and the messages between you and the seller which, should a problem occur, if documented properly all the way through must be enough to prove a case. if you, though, pay via PP you're covered anyway - provided you choose the 'payment for goods' option, which I've always done even when making a purchase from here (and took the accompanying PP fee - for me that +5% is not a money thrown out of the window, should the worst happen...)
hope it helps