When parting sets on Bricklink (BL) make sure you count each & every part (don't assume your set will always match the inventory), many of the catalogue inventories are incorrect, frequently change, are country specific and part substitutions from TLG are getting much more common as are missing parts from MISB sets.
Be aware BL clients are not your average play-builders, many are hardened collectors and very high level build-for-display enthusiasts thus they are much much more finicky about part quality, even new parts that show common manufacturer scratched are often rejected by buyers.
Buy first, you need at least 20 orders/feedback to really be trusted - simply buying several $1 orders (and from at least a couple international vendors) shows just as well as several $50 orders.
Stay out of the forms on BL! Can't stress this enough! Don't even read them, they will do nothing but discourage you from what is a great community. right now BL is being so corrupted by soured individuals it's no longer the happy community it once was before the hacking incident & sale to a commercial enterprise a couple years ago. it's still a great platform - just don't fall into the forum snake pit - apparently less than 20% of members really go in there anyway.
Count your order multiple times, print out the order form & check off each piece as you pull the order, mark a check a second time as you pack the order - things can go bad if you miss a single seemingly unnecessary part or pull the wrong colour if you have the wrong type of buyer.
You need all positive feedback! Neutrals are Negatives - your Percentage rating on the top of every page of your store is a total of Positives - negatives - neutrals (and it displays your count of orders that you made & didn't receive feedback for against your total orders as well). you will always need to take the higher road & be willing to bend to keep the customers happy even though you may know you are right - it's just a cost of doing business there. it's still fun & 95% of orders will be easy & work out well - there's 4% more you may have to curtail your own "knows" just to bring to a happy-for-the-buyer conclusion & there are 1% that are just cut-your-losses 'cause you're in no way going to win.
Take a look at the bigger stores terms, they know what they are doing & have found all the disclaimers they need over years of selling. & remember many of the terms are not based in the real world - things like "I'm not responsible once the package is mailed" doesn't fly - yes you are until the buyer has the item & is happy they can still hit you anyway. "Every order is a binding Contract" no it's not! not in any form of imagination - any buyer can back out for any reason they want - Buyers have all the power, they will always get their full monies back or damage you in revenge - you just have to roll with it, you'll always make up the difference in future sales - just "let it go" when you need to.
Always under grade your parts & over deliver - BL buyers are refined (picky) & they will let you know one way or another... even the least notable thing should be mentioned in the description.
Pack well, spend a little extra time in presentation - it makes a world of difference...
- always send something with the order number on it, packing slip etc. most Bricklinker's order multiple orders from many vendors at a time - don't let yours get mistaken for a bad one from someone else.
- Never pack new & used together - buyers hate that!
- you already sorted your inventory, pack things separately so the buyer doesn't need to - but don't over do it that offends some.
Bricklink is still a viable selling platform & is relatively inexpensive to do so - it's allot of work and allot of time so ya have to be in it for the fun of it as much or more than for the $$$