Welcome to the forum!!
As stated in previous threads, travelling for the right car, is normal. While there are quite a few Zeds on the market, these aren't just motors or value or convenience. You probably have a good idea of the spec you're after for your budget. If buying privately, anything that goes wrong, its very hard to get a private seller to accept any liability. Even if they agree in writing/email prior to purchase. In which case a local garage will be your only option whether buying locally or nationally. If buying from a BMW dealer, you're covered locally. This is the case for my Zed. I travelled from West London to Kent for a car of a my chosen spec. The 12 month warranty and subsequent warranty extension is covered by any local BMW dealership.
Previously I travelled to Cornwall from London by train for a VW Golf V6 4 motion with low mileage, FVWSH and mint condition. Before travelling I agreed with the seller, if the itemised list of queries checks out as you say, then I'll pay such and such a price. Then we confirmed the query list on email. If not, then he had a negotiation on his hands. The paper work and condition checked out. Then closer inspection found some under body damage, hanging off engine covers, and he dropped the price. Deal.
I suggest, do your homework on the spec, get pics and ask questions. Then commit to agreements on your questions so you know what to expect when you see it. Its a buyers market, so you can give the seller a grilling. Any doubts, walk away, there's always more.
Hope that helps. That's what the forum is here for.
Good luck!!