If you are woman in Sub-Saharan Africa and you live and work in a rural area, you are probably a trader. You are likely to be carrying a variety of goods across the border several times per day or week, and to rely on that as a major source of income to your household. You’re probably facing high duties, complex procedures, and corrupted officials at the border – the latter, in some cases, might want to harass you before they let you go through. You may not be able to read or understand what duties apply to the goods you are trading. In this scenario, what is your incentive to go through the formal border post?
It’s probably easier, cheaper, and faster to cross the border informally.