What is the best way to sell a nearly complete large set?
Welcome! Here are a couple of suggestions:

a. Find a review of this set online, ideally one with pictures which shows all the bags included in the set. This will allow you to verify which bags have been opened (you already know which ones are still sealed).

b. Then, download the instructions for 10030 from LEGO.

c. Here comes the tricky part. Find out which steps contain parts from your opened bags, and check if you have all of them. If this is somehow impossible, you have two alternative options:


Open all the bags, build the 10030 and see which pieces are missing, then order those from Bricklink.com and complete your set. List the set as Used, Like New, Built once to validate completeness and you should be able to get a price relatively close to the New price.
Sell the set as Used, 90% Sealed bags, possibly some missing pieces. Depending on how complete it actually is (you won't know) you might get some good offers, especially if box and stickers and such are still present.


To sell LEGO on EBay, you don't need any special priviliges. Just create a listing and sell. However, if you have never used or sold on EBay before, and you have zero or low feedback (&lt;50), starting off with listing a high-value item like UCS 10030 is bound to set off scam-warnings in many of your potential buyers. You'd need to sell other items first before putting this one up for sale. Of course you can always try to sell it via Craigslist, OfferUp, LetGo and other garage-sale apps, but you'll likely get less money for your set (even taking into account that EBay/Paypal will take 12-13% of the sell price and CL/OfferUp etc. take nothing).

Good luck!