I've spoken about our experience on other threads. Our CCV contract was from an international seller (UK) in 2020/2021 and I wouldn't do it again. At the time, I thought it was great since I had already lost contracts to ROFR.
About 6-9 mo after we closed we began getting letters from the IRS. We used Mason title (Marcelo) and he filed the paperwork, did the necessary withholding, and sent the check, but the IRS claimed they never received it. Mason then sent additional paperwork to the IRS with the fedex tracking information -- did not satisfy the IRS. At about a year and half, when we received another letter from the IRS that now had additional fines due to unpaid taxes, I spent hours on the phone with multiple IRS agents and finally ended up with an agent in international affairs/accounts. Agent was mystified why I was having to deal with this (his account reviews were typically for multi-million dollar assessments and sales) and was able to clear up our account (with a 30 day review).
It was basically explained to me that since the buyer is a US citizen, the IRS has the power to levy fines and collect taxes, thus it is falls on us to make sure that withholding is paid. The IRS can't (or the process is much more difficult) do so with an international party (the seller).