In Singapore, if you walk into places such as Sim Lim Square, you will probably see a lot of shops offering data recovery services nowadays. Should you try them ? I think the decision falls back to how much you value your data. In fact, the more valuable is your data, the more qualifications you should make in order to ensure that your data media does not fall into the wrong hands. A lot of time, you only have one chance of successful recovery and the value of data could be more than just saving a few hundred dollars. Do not be penny-wise and pound-foolish.
You could ask if the service vendor has the capability to open up the disk in a class 100 clean lab. If the answer is yes, do not stop your probe here because interestingly, you will always be told that they indeed have the clean lab, just that the lab is located some where and it is not accessible to the public. You should then at least ask for some video or photographic shots. Did you see from the video or pictures that he was indeed the one working in the clean room as shown ? No pictures ? No problem, why not pass your hand-phone or digital cameral for him to take one. Such proof is so easy to come by. If they could not even produce it, be alert.
Ask for a list of testimonials on their service credential. Such testimonials should bear the names of companies and customers. Look closely if such testimonials are fabricated because it is rather easy to say that "XYZ company is our customer and is happy with our service". If the testimonials goes with proper company and user names, it is likely to be authentic.
One should also ask around and through words of mouth, you will be able to make a better selection.
How about data confidentiality ? Look around the place. Do you feel that your recovered data or your original data media is going to be kept safely? Are they going to pass the job to another service provider and increase the chance of data leak? How secure is the working environment ?
If your hard disk failure is one not associated with physical failure, your risk is lower. However, it is still possible that an inexperience service vendor could inadvertently write back the data into the same data space and permanently destroy the original data, hence rendering the job unrecoverable.