Buying Boat Overseas - doable but depending on the boat's current ownership/flag will determine how easy. Local knowledge / language can help i.e.; friends in Croatia.
Example - UK - if boat is flagged / registered - SSR Small Ships Registry - then it is a matter of local Broker arranging for the paperwork to get handled properly such as "de-register" - that document is key.
US Flag - guess you mean USCG - IF - BIG IF, You get a formal document like UK-SSR......then it is pretty straight forward.
USCG National Vessel Documentation Center, Instruction Page
BUT if the boat has not been formally registered in home country - The USCG will ask for "original" MFG, Bill of Sale, etc - chain of custody trail - notarized BUT outside USA a Notary is not always used/avail and if it is - it will require an Apostille Certificate to verify the Notary outside US borders or taken to US Embassy for witness.
The USCG(think military) will go thru the paperwork with a fine tooth comb - ANY deficiency will cause the Application to be suspended for a time awaiting correction of the deficiency(s). There are services that will handle paperwork for a fee or you can do yourself.
The keys = getting proper Documentation/Ownership Papers from Broker/Owner and understanding the USCG procedure completely & thoroughly.
Overall - just realize that "things are different" vs home - might be small or big but preparation, choosing good partners (ie, broker, surveyor, etc) seeking local knowledge or experiences from other sailors will go along way to smooth the way