How long do they think it would take to get your website on the first page of popular search engines?
Do they guarantee results in the time they’ve stated? If they do guarantee results, how do they guarantee them since Google itself states that there can be no guarantees on how long it would take for SEO to show results.
Can they provide some references? If they can, would it be ok with the SEO expert if you spoke to some of their references?
Have they ever worked on SEO for another company in the same field as your own company? If they have, what did they accomplish? Can they provide references to that company in particular?
Have they ever worked with a site developed using the same technology that your site uses? Would they be able to modify the site themselves if they need to or how would they go about it?
What process do they follow?
Do they sometimes use keyword cloaking and other techniques which are frowned upon?
How do they propose to build back-links to your site?
How many back-links a month should you expect?
When would they report their progress? Would it be weekly, fortnightly or monthly?
Do they plan on using Pay-Per-Click? If they do plan on using Pay-Per-Click, how long do they intend to use it and how much would it cost you?
Have they ever got a website banned/blacklisted from search-engines through spamming etc?
Do they understand your goals?
What search terms would they target? It is important that they target terms which are relevant to your business or website because people landing on your website does not generally translate into sales or subscriptions.