If you’ve never worked for a client who also has other people doing the same thing you do, just waityou will. For particularly large or especially competitive link campaigns, it has become more commonplace for a company to try various options, sometimes all at once.
It may not be something that you’re comfortable doing, for whatever reason. If you have expectations in place (such as open communication and honesty) then you may find it difficult to deal with this situation if you’re not “allowed” to speak to other parties.
In some cases, you won’t have a clue that others are working on the same campaign, for example. If this isn’t something you can handle, don’t get involved. If you are involved and then find out after the fact, just do your best to work around it, or, if you feel that you have to, lose the client.
If you have a particularly strong belief in link building without going against Google’s guidelines, for example, you may find yourself working on a campaign that’s also employing people who are buying links. You could be buying links and doing it in what you think is a very low-risk and natural manner, and then discover someone else working on the campaign who is blatantly buying horribly spammy ones that are risky and exceptionally obvious.
The odds of two or more entities working on one campaign and having the exact same mentality about what is and isn’t ok are very low, of course. My guess is that if this situation does arise for you, you’ll find that determining that the good that you think you’re doing may be negated.
Quality is better than quantity and choosing who links to you is just as important as how many link to you. For example, say you sell landscaping and gardening supplies. Having a link placed on a web site for patios or home improvements will bring in traffic that is more likely to be interested in purchasing your product, than traffic that comes from a computer web site or a general links page.
Links pointing to your site from other popular sites can indicate that your site is of better quality and deserves higher ranking. That is, a handful of good quality links, with some engines, is better than 100 links from sites that are not popular.
For example, if one team is doing a big content release and you’re working on emailing and asking for links, time it so that you’re pointing to their new content. For large campaigns, you can move faster if there are more hands on deck. If you can work together, you benefit from bouncing ideas off each other. There can be several different types of link building going on at once (content writing, social media promotions, emailed link requests, etc.)
You should also watch out for any link pages that are generated dynamically. Chances are that such pages would not get indexed soon enough, which means that a link from such a page would not benefit you. Some dynamic link pages are intentionally generated in such a way so as to prevent them from getting indexed. Some unscrupulous webmasters do this to trick you to prevent any Page Rank leaking from their site to yours. Links from such pages therefore do not give you any benefit. Examples of dynamic links include URLs containing symbols such as “?” or “&”.