Be VERY careful with what accessories u sell BEFORE upgrading. With weapons it doesn`t matter as u can always buy the tier one weapons back. Certain accessories like the elemental rings and elemental charms are one offs (except water charms and ice charms where it`s possible to get two). Although u can get the elemental rings back by upgrading and dismantling the charms it is always better to keep em all until they have been fully upgraded and turned into their better forms eg. an upgraded ice ring can be turned into a boreal ring. However please note that you can sometimes obtain a more powerful form of an accessory before finding or buying it`s lesser counterpart. E.g Siltstone ring is the secondary form of the clay ring but if u did not have the clay ring itself but upgraded said siltstone ring and transformed it to its third and final form, Gaian Ring, that would only partially count towards the treasure hunter trophy. You would need to have also have owned and upgraded the Clay Ring.
Again this is just one example but if you`d sold both the elemental rings(BEFORE transforming them into their final forms) and also the elemental charms (remember the charms are the only way to get the E. rings back) you can say goodbye to that treasure hunter achievement trophy for that playthrough. In other words, selling uber rare accessories that can`t be bought or found again messes that trophy up. You`d have no choice but to start again. Extremely harsh and stupid I know...I wouldn`t be surpised if many new people to ff13 missed this trophy the first time round (myself included, I`ve had to start over just for that ONE trophy!...not fun....) the official strategy guide doesn`t exactly warn u it`s missable either!
So here`s my warning and I pray it isn`t too late for u: DO NOT sell anymore accessories, especially if u haven`t upgraded them unless u know u can buy or find them again.
*Edit* I`ve deliberately enlarged the text just to emphasise my point.