I remembered hearing bad reviews about GC, some of which are they replace your gear's parts with inferior parts, but who knows whether is real or not. They been around for decades, maybe not that stingy afterall. Bring your gear down and let them evaluate.
Sell it at SOFT's ads, maybe Carousell would be a good alternative as well.
About re-selling... in general, a guitar with good reputation & strong brand name presence could fetch you 70% of your original paid-for price on a good day. If you think by simply slashing $100 off because you own the guitar for a mere week & thought of selling it away thereafter, you'd be disappointed with the demand-supply outcome. Reality check- why pay $100 less for a used instrument when you can get a fresh one for that difference in price?
If you are in a hurry to sell, and can drop your price listed on soft a little, and he gives you cash. Take it! Often will try to trade, but you have to just say cash only