Hi Karen,
I know it can be very frustrating, especially when funds run out and you get a cert and its the wrong one!!! might as well have burnt my money!!!
I'm currently at a standstill as I need to buy a whole load of certs before I can continue and will have to wait until funds are available.
One tip, is that if you are short of cash, is that its usually easier to find the correct marriage certificate and more can be done with one of those and the census. But you will need birth certificates after a while.
To try and make sure the certificate is the correct one, then contact the local registry office direct. They all vary (check with the area you are interested in on these boards, I'm sure someone can tell you) but some will e-mail and say if they have the certificate or not.
For example: I am having a nightmare trying to find a Henry Taylor born circa 1853 in Prescot area (Lancashire) there are so many that I bought 2 and they were wrong. Instead I was told to contact the registry offices involved (4 of them, unfortunately!!) with his name and the parents name (I am pretty certain of the mother's name as well as the father's due to the census) and ask them if they have anyone who matches this. Though they will generally only search 5 years for you.
3 of them e-mailed, with one giving me the parents of all the Henry Taylors in their district. Which was great, but non fitted.
Finally I am having to write to the final one (liverpool) as they only do postal enquires. They only check if you send a cheque, BUT if they don't find it they will send the enquiry on, or return the cheque.
I haven't done this yet, but at least, even if nothing comes up, I haven't wasted any more money. If I do get the cert, then it will be the correct one.
Sorry, bit of a waffle, but its a way of making the pennies stretch a bit further.
Hope that helps.
Cindy