^ You have to use a middleman to buy from Yahoo Auctions Japan. I've never tried those sites you asked about, I've bought my resale tickets from YAJ and ticketcamp using different middlemen. I don't remember the contact details of the first one I used, because it was a long time ago, and I'm not even sure if he's active anymore.
I also used celga this year, some people on this forum say they're unreliable, but I personally had a good experience with them. They took quite a while (2-3 days) to buy the tickets though, so if you expect the ticket to sell out very fast, I'd recommend you to find another service.
KarenPang recommended me
http://japanauction.byethost11.com/ . I used their service since by the time celga tried to buy my ticket for another artist, someone else had bought it already (the demand for the tickets was quite high), so I decided to try KarenPang's recommendation and I'd say this service is really good! They replied pretty fast and everything went very smoothly. I think it's more expensive than celga though.