Measure the journey as well as the shelf
Suppose the space is 82 cm wide and the bookcase is 80 cm wide. Check the depth, height, skirting and any obstruction that could prevent it fitting against the wall. Then check the car opening and the route from the pavement to the room. An 80 cm item can fit the room and still fail at the hatch.
Give the person at collection a decision rule
Agree that they can accept the listed bookcase up to $45 if its shelves and joints meet the description and it fits the route. If collection costs $12, include it in the discussion. A discount of $5 does not solve an unexpected $25 transport fee.
Leave room to walk away
If the bookcase differs from the listing, send a photo and the new price before taking it. A lower price does not fix shelves that cannot hold the books. Keep the seller’s message and the agreed collection details until the item is home.
If the piece can only travel after disassembly, ask whether it was designed to come apart and whether the needed hardware is present. When the answer is unclear, send the details home before accepting. A photo of the actual measurements often makes the decision easier than a description such as “slightly larger.”