Don't just trust the seller's smile and the photos they send you - buying from a distance is already risky, so checking the paperwork is non-negotiable. Before you even think about transferring the title, you need to know if the car has debts (lien or unpaid credit), if it comes from a serious accident or if it's simply gone missing from German authorities' records. Ask for a complete report from the Kraftfahrt-Bundesamt, it's the German federal registry and it's your best friend there. Also check on the insurance data side - in Germany that exists and it costs money but it's really worth it.
Now the thing nobody ever mentions: before you sign anything, contact the Belgian registration center directly (SPF Mobilité) to find out if a German Golf 7 will pass their emissions standards without having to modify it. Certain years, certain engines require certification that costs a fortune or it's just impossible. I know someone who rushed into a similar deal and ended up with a car she couldn't legally register, stuck in France. So really, call before, not after.
And then some purely practical advice: have the car inspected by an independent mechanic on site in Germany before you buy, not after delivery. Yeah it costs a few euros but it's nothing compared to finding out the gearbox is dead after you've already paid for it. Make sure too that all the service records are there and that the mileage is consistent with the wear and tear.