Altought there's a lot commons sense and SEO knowhow out there on linking and link development, some major rules shall be outlined for the websites that I will link to from the presell pages

1. Website must be legal, and must only sell / feature legal products.
2. Website must be suitable for a family audience.
3. Website (or URL for links) must be recognised by the main search engines - that means cached/indexed
4. Website must not contain any material that could be deemed offensive.
5. Website must not be pornographic or contain 'adult' content or products, except for presell pages hosted in the adult industry itself
6. Website must not sell pharmaceuticals or related, except for presell pages hosted in the pharmaceuticals industry itself
7. Website must not sell or feature weapons including guns, knives, etc.
8. Website must not provide online gambling, except for presell pages hosted in the online gambling industry itself
9. Website must not be a copy or near copy of DMOZ or any other website. No Duplicate content allowed. If in question, then these duplicate content check tools 1 and tool 2 shall help to judge if the duplication is below 60%
10. Website must not contain Spam, Scraper Content or any other kind of rubberish, automatically generated stuff
11. Links will not go out to affiliate programs, redirects and such
12. The Presell Pages will not host signup forms, banners, images, logos or any other kind of adverts for you on it - and only talk in a distance 3rd person view about your business
13. Websites must not take part in a SEO Contest

In addition to that the site's owner has the right to always reject writing and linking to you for any reason, which would then result in a full refund for you.