What to expect if I import an amp and preamp from a Japan seller via US eBay

From my experience you should expect to pay up to 10% depending on the state you live in. I shipped a dac to Italy for updates/service and when it crossed the border on the way home it was reported. A few months later I received a bill from the state requesting 10% of the value I declared when shipping it.

Fortunately I had written all of this (returned for service) on the international waybill when setting up the shipment. The tax collector could have easily seen this but they prefer to make details YOUR problem. The waybill was used as a means of avoiding the tax when they came to collect. 
 

If it were me I would purchase with an American Express card to ensure there is automatic buyer protection and then contact DHL (or whoever you prefer) and arrange for the shipment yourself. At least that way you have control over the information given (declared value and replacement insurance). The carrier representing you should also be required to verify the item exists (is actually in the box) in the case the seller was planning on sending you a case of cinder blocks.

I take good price over any warranty simply because I don't believe anybody or anything.

Equipment repair is the issue today, because it's EXTREMELY hard to find knowledgeable technician. They're all either too old, dead or not found anywhere near. 

With today's level of education, unlikely there will be any new ones and you might want to travel abroad to the countries that still have politically uncompromised education

Shipping is free via Fed Ex.  The seller tells me FedEx will contact me if fees are necessary and when they are paid FedEx  will deliver to me.

Good point about who will do repairs.  I will ask my usual good fellow if he will repair.  Otherwise there is a high end sort of repair facility in the LA area.  I’m near San Francisco.

Here’s one more thing that concerns me.  Electrical voltage is different in Japan.  I will need to use a down transformer.   No big deal, people use them all the time.   However, someone made the remark that they degrade the sound slightly.  That’d be a big blow to me.  After all, the sound is why I want to buy the gear.

A quality step down transformer will make no audible difference to the sound. But as someone mentioned if the amps are Accuphase it is not difficult to convert to US voltage.  It's the same with some other non US manufacturers.

I would make sure you were dealing with an extremely reputable dealer in Japan, such as Hi-Fi Do from whom I’ve purchased in the past. In retrospect, I would be reluctant to do business with a dealer from Japan, and would find something here in the USA which will satisfy you within your budget. There are just too many things that can go wrong, Including damage from shipping internationally, customs duties, etc., and I don’t think it is worth the risk or the potential headache. Just my two cents based on years of experience,