20% Handling fee charge

On Saturday 21 November I bought a Bosch fuel pump for R1 845 for my Volkswagen Kombi, hoping to replace it the same day as my brother was coming over to help. On taking out the non-working pump we found that it wasn't the pump but the connector that was broken. I returned the pump to Goldwagen on Monday 23 November only to be told that I would be liable for a 20% handling fee (R369) for a product that had not been installed. After negotation the fee was reduced to 10% (R185) which I still feel is excessive as the pump was returned in its original state.