the time to check out an agency is before you sign the contract, not after. they are legally binding contracts and are not easily cancelled. and if you notice that many have large cancellation fees if you leave the contract, and that is even before you come to the us. or go to any other country.
please take the time to do a search on the agencies that you are considering. if the offer sounds too good to be true, compared to others in the are, then it is.
have seen agencies not live up to their promises, as well as those that follow every promise exactly.
if you have any doubts, check with the us embassy where you are. they are very aware of what is going on with some agencies.............but do not sign until you have valid information in front of you.
and if any agency guarantees approval in a certain number of days: run
no one has any control over what uscis can and will do, and they can't make a promise that will be met. right now, the retrogression is in place, and nothing past the i-140 is getting approved. not one thing, no matter what they tell you.