Is it permissible for someone who is embarrassed to ask for a direct fee to add the cost of transportation and a small amount for his effort to the price of computer components he buys for his clients, so that the total amount he takes represents his fee?

If you buy the components and acquire them, then sell them to customers, it is permissible for you to add profit, and you are not required to inform them of it. Rather, it is sufficient that they know the total price. However, if you are buying for them by agency or commission, you must inform them of the price of the components and the amount of your fee or commission. It is not valid to use shyness as an excuse.