Here is a thread with some more Japanese middleman services: www.elitefourum.com/t/japanese-marketplace-list/21709/1
I’ve personally used Noppin the most, 20+ times thus far I think. They can be pretty expensive unfortunately, but I never had any issues. They package very well; I can combine orders for up to 60 days; won’t have to pay anything unless I win an auction; and the few times I used their customer service they were very helpful. Unfortunately Noppin has been closed since mid last year. At first it was due to the pandemic, but it seems they’ve taken this opportunity to update their website which is still ongoing apparently. The website mentions it will open again on June 1st, but I would take that with a grain of salt, considering it originally stated February and has been postponed 2-4 weeks into the future each time they’ve reached that deadline.
My experience with Noppin thus far can be found here.
For the past few months I’ve been using Buyee, since it’s integrated within YJ. Thus far I’m not too much of a fan in comparison to Noppin, although it’s a nice alternative nonetheless. If I compare the two, the main two pros of Buyee over Noppin are: they’re currently open and Noppin is closed 
, and Buyee has cheaper middleman fees (for both it’s 500 per product, but with Noppin you pay an additional percentage for everything over 5,500 JpYen). Shipping fees are the same; ease of use is roughly the same; and you only pay after you’ve won on both Buyee and Noppin, so that’s the same as well. Buyee’s packaging is ok, but nothing too write home about, unlike Noppin’s amazing packaging job. And one huge disadvantage of Buyee in comparison to Noppin I’ve experienced: your max bid is 300,000 JpYen.
Since Noppin is still closed, I might try FromJapan in the near future if I want to buy something from YJ, since two people above recommend it. 
PS: I know this is about Japanese middleman services, but harum.io for Korean webshops (i.e. tcgbox.co.kr) and superbuy.com for Chinese webshops (i.e. beehivetcg.com) I can also recommend. 
Greetz,
Quuador