Sometimes it makes more sense to start again rather than to try and fix what you’ve got. That applies in website optimisation as much as anywhere else.
Sadly there are plenty of sharks in the SEO pool, and taking their advice can cost you thousands of pounds. I’ve recently spoken to a couple of people who’ve spent a lot of money trying to fix sites that are not ranking well. Investigation soon revealed that they’d had some pretty dodgy advice in the past and had been penalised for unethical optimisation techniques. Now you can either sort out the problems so you’re whiter than white, do more good quality optimisation, and then sit out the penalties until you come out the other side; or you can chuck that domain in the bin and start over.
Sometimes it may be worth sitting it out if the penalty looks like it might eventually end, but other times if there’s no sign of improvement it may be throwing good money after bad. If a previous optimiser has really made a mess of your site with doorway pages, hidden text, duplicate text, etc. it may never recover no matter what you do.
A new site on a new domain will take a while to rank well – 6 months is not at all unusual before rankings start to come through on Google and to get anywhere useful may well take longer. You need to decide if you can survive on MSN and Yahoo results (which usually come through rather sooner) or if you can afford to use PPC to get the traffic you need until natural listings start to kick in.
It can be a tough choice but it may be better to learn the lessons of the first site, apply them to the new one and move on with the advice of a trustworthy SEO.