I've used Sharp Service in the past but haven't heard back from them on my most recent enquiry and have also read some reviews of recent shitty service.
Should note that it's not for an auction but for a simple store purchase.
I'm in Japan right now and happy to proxy for people.
I live in Tokyo and this would be a side project. I speak fluent Japanese, so I can buy stuff that might require a bit of navigating/back and forth with stores.
I can also go to stores if the stuff you want can't be bought online. I'm a single person, not one of the larger proxy services but you can expect more tailored service from me (I can take pics and send them to you and repackage stuff as you want it).
Let me know if you're interested.
FromJapan is good and easy to use but pretty expensive and they will not undervalue your items. Shipping is also pretty expensive, 3000-4000 yen for a shirt or jumper depending on the weight (I am in New Zealand). The global Rakuten website is pretty good if you don't want to use a proxy, but in my experience they assess the shipping costs once you place your order and charge your credit card without confirming. Sutocorp looks pretty good but haven't used it yet. Sharp is long dead.