What is recommended percentage of markup for retail?

There is no recommended percentage. The markup will depend on market conditions such as the nature of the product, the cost of substitutes and complementary products, the retailer's cost structure, competition from other retailers. Essentially it is the maximum that the market will bear. There may be times, however, when the markup is greatly reduced (a sale). This may be to get rid of old stock so as to finance new lines, or as a loss-leader to induce customers to come into the store.