Marktplaats supports Paypal. But whether it's possible depends entirely on the seller. I guess many non-commercial sellers may have no clue how to use Paypal. Other options are iDeal (a Dutch system), pre-payment via bank-transfer and of course cash. NL is a small country so items are often picked up in person. Sometimes this is the only option ("alleen ophalen").
Most people can speak English. If you're willing to pre-pay by bank transfer and pay for shipping, there's no reason why a reasonable person would refuse to ship abroad.
Of course pre-payment is generally not safe and bad advice. There's nothing you can do if things go wrong. But personally I've done it for items below a certain price that are not typical scammer's items. Use your own judgement.
I could do some nice business on marktplaats.nl but I can also tell some hair-raising stories.
As everywhere it depends on the salesman, you will have to bring confidence in any case when you do pre-payment without having seen and tested the item.
