When choosing a Service Provider take into account their experience or inexperience.
Generally, the more experienced Service Providers will charge more because they have a proven track record. On the other hand, if they don't have much feedback you may be able to get a better deal just because they want the positive feedback and they do not have the track record yet that the more seasoned Service Providers have.
Just because someone offers you a low bid it may not be your best match. Consider what it is that you're shipping and how valuable it is to you. Also, do your homework in regards to legality, licensure, insurance, etc.
Finally, you may get better deals if you can be flexible with your shipment and pickup dates. This will allow more Service Providers to place bids and give you more choices as to who you want to ship your items and how much you want to pay.