Most ResinSoul/Bobobie dolls need a restring right out of the box, or at least a tightening, as the elastic is notoriously loose and/or crappy.
One diagnosis I've used is to pick up the doll by the midsection. If he or she flops like a ragdoll, and is loose enough that this flop shows the elastic in the torso, or seems to be coming close to showing, they probably need to be tightened. Every one of my RS dolls got a restring, except for Seona (my double jointed Jun) but that's because he's more of a display doll, due to his heavy paint job that chips if you so much as look at him funny >.< My Ai is ready for another restring, because the strings I used in her were too small, and stretched out too easily.
Sueding also helps RS/BBB dolls a great deal, but it's not necessary. My girl Wu poses quite nicely now that she's had a restring.