Another faulty flash bought cheaply and suffering from the usual problem - folk leaving non-rechargeable type cells in the battery pack, which leak and start corroding the terminals. Aside from this, the rest of the unit looks to be barely used. Cleaned up, and it works well. Just a pity they did some scraping about the top of this terminal, which allowed the corrosive liquid (usually alkaline rather than acid) to penetrate and lift some of the plating, which may reduce the overall value.

We all do it, but try not to leave non-rechargeable type cells/batteries in devices. And also be aware, before throwing out things that may appear to have bad damage from such leakage, there are folk that may still be able to sort it... and sometimes that can be surprisingly easy.