I have an ecommerce site (I'll call it Site A as there are other sites involved) which ranked well in Google from 2003 and steadily improved over the years to around 3,000 uniques a day but I have a feeling it has been suppressed since March 2008 and can't figure out if it's real or just my imagination. I can see loads of potential causes but I don't want to change things until I'm sure we have a problem. I'll try to include every factor I can think of. Here goes...
In June 2007 Site A lost about 25% of its' traffic from Google after the major update around that time. It looked like an OOP as we lost rankings for exact phrases while retaining rankings for non-exact terms. Before we figured it out things got worse in October 2007 when major pages from the site were being removed or -950'd from the results on a daily basis. At the time we had about 30 links in the footer to internal article pages and the -950 thread on here suggested that could be culprit so I removed them. Immediately (the next day!) our pages started to return to their former positions and even our pages that had been suffering since June 2007 could be found again for exact phrases. Within two weeks traffic returned to it's pre-June 2007 levels. Problem solved so we thought.
In December 2007 I hired an SEO to check over all my sites for any potential problems. He felt Site A looked okay but recommended we improve our trust rank with some good quality links, so we choose some phrases to target and set about it. He did have a concern that linking from two of our other sites may be a problem (Site B and C which I'll come onto later) but wasn't certain that removing the links would do more good than harm so we left that alone.
In Feb 2008 we began to notice our rankings for the pages we had focused link building on gradually falling from their page 4 positions and dropping a page each week or so. This didn't have any noticeable effect on traffic but was a concerning sign, especially as all other rankings remained exactly where they had been for years.
In March 2008 we had to change hosts from our Canadian hosts and decided on a US company. All our sites have .co.uk domains and are aimed at the UK - the sites were hosted in the UK on shared servers until 2005 when we moved them to two dedicated servers in Canada and all continued to go from strength to strength for years so we had no reason to believe server location mattered. As before, all domains were on separate, non-consecutive IP's.
During April 2008 traffic dropped by 30% and rankings on the pages targeted for link building had dropped to effectively nowhere so at the start of May 2008 I called a halt to the link building. By mid June traffic had returned almost to normal (about 10% below) and the link building pages recovered to about page 10.
The peak season for Site A is November and December. During these months in 2008 our traffic lifted as normal but was constantly 25% lower than in 2007. I also noticed that for certain long'ish tail search terms our pages were bouncing in and out from high page 1 positions (which we'd held for years) to nowhere in 2-3 day cycles. The keyword density for the bouncing phrases is quite high but no higher than other phrases which are not suffering. The site content is mainly product information so certain words can be inadvertently repeated alot in some categories.
In Jan 2009 traffic has remained 25% lower than normal for this time of year and certain pages for certain phrases are still bouncing in and out.
A few other things to mention......Site A grew from 200-500 products (one page for each) from 2003 to 2006, and continued growing steadily to what is now around 2,000 products. So watered down PR could be an issue.
Site A has a menu of about 50-60 text links, all with relevent anchor text. I've read about mega menus and the potential problems but I'm not sure if ours is big enough to fall into this category. It's always been like that.
Interlinking is the other potential cause I haven't gone into in detail yet. Site A is our main ecommerce site selling products in a niche. Site B is an affiliate site (set up before Site A) featuring all sorts of products but one of it's eight sections is aimed at the same niche as Site A and contains our products and those of one of our competitors, deep linking to the product detail pages and category pages. Links to our competitors products are through an affiliate agency, links to our products are direct to Site A. Within this section of Site B we also link to various relevent sites on every page (including Site A).
We also have Site C which is another affiliate site but purely in the same niche as Site A (set up before Site A). It contains our products and our competitors and links through in the same way as Site B.
Site B and C link to Site A, but Site A does not link back.
The only other thing to say about Site B is it has always been my experimentation site and consequently does get a rough ride in Google (lots of chopping and changing, old pages ditched, lots of new pages added occasionally). Most of the content on Site B is provided by a third party price comparison site and we have a web directory where you can advertise for free in return for a link to us, or pay to be listed. All outbound links have been 'nofollow' for 6 months, except those to Site A.
I spend ALOT of time reading threads on this site so I know I've mentioned loads of potential causes (US hosted UK sites, interlinking, mega menus, duplicate content, link building, over optimisation, and so on). I've even considered the possibility of DNS hijacking which seems to match with a consistent 25% reduction in traffic. My sites are potentially guilty of them all but I'm trying to rationalise this into what's realistic.
I've always tried to keep Site A 'clean' as it is an ecommerce site and our main source of income. Everything (except the footer links - hands up to that one) has been done with the visitor in mind. Over the years that approach, and some basic optimisation, have got us a long way.
Site B is another story. That has always been an SEO testing ground and traffic fluctuates massively. Google has shown encouraging signs that suggest it could fly if we can clean it up (it's good now but there is a lot of historical shrapnel laying about).
Site A is the priority though. Are any of these issues causing a problem, is it a bit of everything, or is everything fine and I'm just being paranoid?