There are many reasons why transporters can offer discounted rates. It can come down to the number of items they are moving at once, if they are looking for back runs and even if they have busy recently.
Collecting several items that need to be collected and delivered along the same route allows transporters to keep the price down for each individual item. Some will even store the item for a day or two after collection to fit it's delivery in with other jobs on the route.
Some will place a low bid on a job that covers their fuel costs on the way home from another job, this also allows them to give a discount.
Many other transport providers have plenty of regular work from their own private customers, this will be their major source of income whilst they give discounts to our customers.