Will the set still be consider new if i open the box to check if all the bags are there and then close it? will not open the bags thanks for your time and knowledge

I've been wondering the same thing, the bags are still sealed, although I think it's still considered somewhat used.

If I was selling it on a site such as ebay, I would list it as new and state that the box is open in the description.

If I was selling it on a site such as ebay, I would list it as new and state that the box is open in the description.

Yes, that is the proper way to do it. If the box is in great shape and all the parts are accounted for in sealed factory bags, then the set is still new, but it is not considered "Mint In Sealed Box" or MISB. It can be considered New In Box or NIB. For a serious collector, it drops the value of the set, but for most buyers it means only a small decrease.

Whatever you do, never tape a LEGO box shut with masking tape or scotch tape. See if you can salvage the seals on the box. Sometimes a hair dryer is a good way to warm up old seals and reapply them.