BUGSY575

There aren't a huge number who have ordered their custom boots, and fewer still from Europe.  I'm sure the store can answer your questions as to shipping and import duties.  Likewise as to whether they're still doing custom orders.  Seems simplest to just ask.
 
Other than those possibilities, however, no, there are no hidden costs.
 
The off-the-shelf sizing is going to come from wherever they keep their stock.  The custom orders, as I said, you'd do best to ask direct... even if someone else from Europe has ordered the custom boots, it would be a shame to find out the hard way that they've changed their policies.
 
One thing I would definitely advise is be prepared for it to take longer than estimated.  That seems to nearly always be the case with vendors these days, sadly...

I’m not sure about shipping to Germany but my boots came straight from their store in Georgia (I think) to Pennsylvania and took about 4 days all together. Customer service was great when I emailed a question, and the boots fit nicely and seem well made. I wear a 12 but sometimes I’m a wide. I ordered the 12 regular and they are perfect.


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Agreed, fit is very important! Make sure you get a pair that's right for you! 

You can usually find equestrian boots on eBay and Etsy for a reasonable price, the trick is condition and fit. The other option is going custom with Mux (my preference) or Hessian Antiques.

Standard riding boots, used by officers, cavalry, and anyone who rides "english" for a couple centuries.

^^ That.  Very basic riding boot pattern used all over Europe (and the US) for a long, long time.

I've only worn my officer on a couple troops so far. All I've gotten with that is "what military do you represent? Oh! Star Wars! Right!"
 
But in my Guard costume, I usually just get "Red Guy" or "Vader." I'm always flabbergasted by being called Vader. Have these people paid any attention to pop culture? I did have one guy in his 40's run up to me once, though, and say "Imperial Guard! You were my favorite growing up!" and took a selfie with me.