Personally, I would'nt be risking it

New, inexperienced seller, selling pricey items, to a buyer in Belarus

I smell red flags

What is your gut saying ?

Your postage specifically excludes Belarus, so I would tell them no.

Way too many problems I think, to make an exception.

To answer your questions.

They would do it and send a request for a total.  In which case you send them back an invoice with the adjusted postage included, then they pay based on that.

Australia Post don't send to Belarus, so you would need to find a courier.

But, The above was for info, I just wouldnt send to Belarus,  sounds dodgy as Bat poop.   But I no longer send anything overseas,  it's just not worth the hassle.

Definitely not. Don't even consider it. Block the buyer and make sure you update your buyer requirements that blocked buyers can't contact you, or buy from you if they are outside Australia.

Belarus? No... no, not a risk worth taking at this time.

Can they not source a mattress heater locally? Red flag.....block....