They ouright refuse to meet you where you feel comfortable and safe.
Typically thieves will not meet you in a populated area and may ask that you go elsewhere.
In a parking lot far away from customers, cameras and streets for example.
Bring a friend with you to the location if possible.
Don't let your need for money or an item blind you against reason either, do not meet people super late.
Someone I know got robbed out of 3,000 a couple weeks back.
The seller asked them to meet in an empty parking lot at 1130p to buy / test a car.
Setting up near or at a police station is always advised for bigger transactions.
If you are unable to meet during the day that's unfortunate.
My advice in that case is to ask someone you trust to make the deal for you or use the shipping feature if the item is small enough.