Buying a Japanese blade with no certificate. Great deal or terrible idea?

I’m in Japan and being offered this katana from a reputable dealer at what seems to be a great price? (I don’t know much about swords but it’s middle edo era). Trouble is it doesn’t come with a certificate of authenticity(I was told the previous owners didn’t want to shell out for one) and has some dirt/rust meaning I’d need to pay for at least a partial cleansing. Don’t know if buying it (would be about 3,500 with shipping home and a partial cleansing) is a terrible idea and if I could get a better cleaning in the United States. Any guidance would be appreciated