When rankings dip what's the best diagnostic procedure?

[Nightwing]

Bonjourno from 10 degrees C lighly raining Wetherby UK

Every so often SEO feels like a game of snakes & ladders. One minute your rankings go up and then then within the click of a mouse they drop back down. Like a Greek play you begin to feel our mortal lives as SEO pundits is controlled by the Google Gods.

A case in point is illustrated here in this graph:
http://i216.photobucket.com/albums/cc53/zymurgy_bucket/lincoln-drop_zpseeb04690.jpg

Now if i want to explain why the rapid dip has occured for target term "Lincoln Solicitors" here's is what i'd do:

1. Go to webmaster tools and check for crawl errors

2. See if a Google algo change has changed the rules of engagment

3. Check another site administrator hasnt tinkered with the original layout

But i wonder what process do other SEO practitioners follow to explain to a disgruntled client - "Why have my rankings that i pay you to look after nose dived?"

Any insights welcome:-)

[Nightwing]

N.B - Looked into webmanster tools and found this:
http://i216.photobucket.com/albums/cc53/zymurgy_bucket/server-errors-langleys_zps10c62870.jpg

Would i be right in suggesting this has played a significant part in ranking demotion?

[Marcus_Miller]

Well, firstly we can do a simple check against dates of known algorithm updates and see if that matches the drop.

So, you have a good rank on 17th July and have dropped at the next rank check on the 26th July.

Panda 3.9 hit on July 24th so there is every chance the site was flagged in this update so that would be my first port of call to see if this seems a likely case.

It's very hard without a link, but start with the dates and if you find something that seems like it could be the case then review the page to see if it is weak, or a near internal duplicate or some such.

I have checked the 14th result for that search term and the page is pretty weak, I am not sure if this is your client but if it is (first two letters of url are www.bm) then these are very weak pages with little to no unique content beyond the address so this is a page created pretty much entirely for search engines so is typical panda fodder.

So, to resolve? Make this page better along with other similar ones and if that is the case, then it should help resolve matters.

Hope that helps!
Marcus

[MagicDude4Eva]

I would check where those 500-errors originate from. Your website does not handle errors well do - i.e. the link to "/About-Us/Partner-Profiles/Partner-Profiles/Anna-Mosey.aspx" throws a 500 and should really be 404's or 410's.

When I do the search (from South Africa), the search term is on page 1, 4th position.

I would perhaps have a look at validating HTML as well - found it quite strange that the anchor-texts in the have so much trailing whitespace.