Ok I've read the french thread (thanks MisterRios!) and in short people were extremely satisfied with them and praising them for top-notch service for about 2 years (thread started in 2010) until last summer when lots of people started complaining about them being unreliable: having to wait for months to get their orders (one of them waited for 7 months and still got nothing), receiving bags that didn't fit with their ukes, not getting reimbursed when cancelling their orders or returning items, paying express delivery and getting the uke after a very long time, or even getting used string packs instead of new ones etc. They say the seller often wouldn't reply to their attempts to contact him, so they were furious (one said he had left 15 phone messages and sent 10 emails). Then earlier this month, people start posting satisfied comments again but other people are still having bad experiences. It seems originally there were more complaints on the thread but the moderator kept the ones that seemed genuine and coming from people who had directly dealt with them.
It seems that the store constantly has problems with back-orders but still keeps unavailable models on their catalogues. Basically, I think they're selling people ukes they don't have. Which is ok if you know a stock is coming soon, but not when their production has stopped and there's no way to ever get them again. Seems both cases are happening here. Sometimes they still do nice gestures such as sending a more expensive uke with no extra cost. When they reply they are pleasant and blame their computing system, but they don't reply much. Main problem is the lack of communication, it seems. They won't tell you when a product is out of stock and won't reply much to emails (or phone calls, or text messages) for whatever reason.
Some people said it could be that every single person who had ever had problems with them ganged up on the thread and that satisfied costumers remained silent. Could be. Still not a very good business practice IMO. They owe their costumers better communication. There's enough really good online-sellers around not to have to deal with unreliable ones like this one. Best to avoid them I think personally. Looks like they started really well but got off-tracks after a while. Maybe they got overwhelmed and didn't manage to deal with it? Such a shame.
Someone said they were successful in contacting them when going into their account to edit their order and leaving a message in the comment window though. Might be worth a try?
Good luck!