Any advice on how I could purchase (bid) on a frameset, on Marktplaats, from the USA?

There are proxy companies that handle this sort of thing. The seller ships the item to their warehouse in-country, and then the proxy company ships it on to you in the USA. Some proxy companies also handle the payment process, while others will expect you to arrange that yourself between you and the seller. Inevitably some sellers will not be interested, but most who are willing to ship in-country will probably agree.

The obvious way would be to open a (free) account on Marktplaats, message the seller by using the "Bericht" (message) button, and see what happens. Most people selling interesting framesets won't be too surprised, I'd think.

Another approach could be to get in touch with an experienced local trader in such wares, who might be willing to handle the pickup and shipping - or even the whole transaction - for you. One man who comes to mind is Frankie van den Elzen of Thevintagebicycle.com. Nice guy, knows his stuff and his prices are reasonable, IME.

-----


WARNING!

MARKTPLAATS is a highly dangerous site.

whatever term you enter in the search window there shall be untold thousands of returns

entire days can pass by unnoticed whilst exploring the site, especially for those with multiple interests...


-----

Indeed you might open a free account on Marktplaats and try to buy the item of your choice. But perhaps a Dutch seller might not want to handle the shipment to the US. For sure I would not want to organize shipping a frame to the US. Frankie van der Elzen I also recommend, or else Frank Weegberg from Classicsteelbikes.com.
Just from curiosity, what frame sparked your interest?

The Kessels Merckx frameset

There are two framesets on there atm

The guy who's offering the complete bike claims to ship worldwide.
(but ime he's a bit of a flake unfortunately)

I can vouch for Frankie van den Elzen, btw, very reasonable as well as reliable.

https://www.dcisite.be/en/dci-news/Kessels-A-Story-CP Thanks, looking at the 61cm frameset, it appears the frame would have 531 main tubes, and forks, with other for the rear triangle.