I personally look around heavily for the best deal before doing any purchases online.  A smart consumer will do this as well, there are numerous reasons why it is smart to shop around and carefully select the company that you want to deal with on a variety of factors. 

Factor #1.  Initial Product Cost.  For this article, I am going to use a camera as the item I wish to purchase.  I have found a website that offers the camera at a very low price.  However, while looking for the lowest price for the camera itself I also need to carefully consider some other factors before completing the purchase. 

Factor #2.  New vs. Used vs. Refurbished.  If you are not picky about the item being brand new in the sealed factory box, you are often able to find open box sales or even remanufactured units online at great deals.  These typically also include a warranty so your purchase is still covered from defects.  If you are not picky about the unit being brand new, some stores even offer used units, the used units typically have no warranty.  EBay is also a good place to find used units. 

Factor #3.  Sales Taxes.  Depending upon which state, you live in, and where the merchant you are shopping with lives, you may have to pay the sales tax.  Depending upon the tax rate in your area this can increase the price of the item by as much as 10% possibly more!  Some merchants do not charge for any of their items, others only charge residents in some states.  Find out the merchants standing on charging residents of your state sales tax. 

Factor #4.  Shipping Charges.  This is something that depending upon the size, weight, and shape of the item can add massive charges to your total.  Some merchants offer specials such as penny shipping and even free shipping depending upon your total.  Other merchants offer free shipping always.  This is another great way to save good money on your purchases; however, in the quest to save money, you still should demand a tracking number for your package so you can make sure it is delivered properly with no problems.  No great deal on shipping is worth it if your package does not arrive to you. 

Factor #5.  Rebates.  I have always found rebates to be a bit of a sticky subject.  Some merchants are great about honoring them, while others are a bit sketchy about paying the rebates as they claim.  I tend to ignore the rebates when figuring the price of the item, and just view the rebate as extra free money if I receive it.  You should check online reviews to see how well the merchant stacks up for paying the rebates that are submitted.  Some consumers have great luck with having the rebates paid, and prefer to subtract the rebate from the total price of the item.  The choice in how to handle rebates is up to you.  I have personally found the manufactures rebates tend to have a much higher success rate of actually paying as promised. 

As you can see each of these factors greatly affect the price of the item you choose.  While one merchant may offer free shipping while charging sales tax, another may charge for shipping but does not charge sales tax.  This is a game of numbers that is often difficult to play.  An additional word about shipping, some stores that have physical locations as well as online business often have an option where you can pick your item up.  If your selected merchant has this option, you are able to save the shipping charges.  However, the drawback is, if they are local enough to allow pickup, they are most likely required to charge sales tax.  Good luck price shopping and enjoy the fruits of your success.