One may need to check out what kind of data guarantee do the vendors provide?
In case of partial recovery, will the vendor still charge you a fee? Are there any hidden costs not mentioned? Do they published on-line pricing guide? Do some of the free services appear suspicious?
Some companies will charge you for the recovery fee, diagnostic fee etc even if they are unsuccessful. The more desperate and urgent you appear, the higher fee will they charge. You should not have to pay for anything when nothing was recovered. In fact, you should not pay when your required data is not recovered, even if they are successful in recovering your not so important data.