On-line/in-store price discrepancy

A 50ml container of garden pesticide which is costs R129.99 on Mica's online platform, is marked R169.99 in store. Management had no rational explanation for this discrepancy other than saying that if ordered on-line, the courier fee would bring the price up to what they were charging in-store. This is an unacceptable explanation. Surely, they cannot justify charging an extra R40 on each 50ml bottle on in-store purchases of the product. I eventually purchased the same product from the nearby Stodels Nursery for R149.99