I've written on this topic before, so I won't repeat myself in detail here. (I don't know how to search for my previous posts on this point, but there must be a way.)
The short version:
• Unless you are really confused by the process, or your case is unusually complicated, you can do it yourself.
• Most of the work is getting documents and information, and putting it into the correct forms. The consultant cannot do that for you.
• Where you are uncertain, ask for advice from those on this forum who have succeeded in getting their visas. Their successful experience is a better guide than the unproven advice of a consultant (You have no way of knowing whether the consultant’s advice is really good, or he just says it is.)
• Once the application has been submitted, there is very little for anyone to do. The consultant will say he is “representing” you, but when asked what he actually does to represent the client, the ones I interviewed had very few concrete examples to offer. Beware vague promises without concrete examples
• If you do hire a consultant, never pay all the money up front; pay in stages, so that if he stops being useful, you can hire someone else with the remaining money.
• Look carefully at the contract, which usually favours the consultant in cases of disagreement, and request changes if necessary.
• Ultimately every decision is a leap of faith, since you can’t know in advance how the consultant will operate. But you can cut down the areas of ambiguity by having a contract that specifies in detail what the consultant will do in each stage, and when each progress payment is due. Most will balk at this arrangement, but keep on looking for those who are sufficiently confident you will be satisfied that they don’t need all money up front.
• Good luck.
