Bad practice
As well as over optimisation, the major search engines (and Google in particular) "frown upon" various SEO practices, as they are obviously only being implemented in order to influence their SERPs rankings.
These practices range from old techniques, such as "keyword stuffing" and "hidden text", right through to things that have been seen to still work occasionally, such as "cloaking", which is the practice of developing different content for the search engines (i.e. keyword rich) than for human site visitors.
Link building practices can also be frowned upon, including that of "guestbook spamming" - whereby a link to your site is placed on multiple open-access guestbooks or forums, in order to increase your site's Page Rank; and buying links from high Page Rank sites - which Google has explicitly stated it does not consider being acceptable within its guidelines.
Evidence of bad practice could lead to your site being "banned" from the search engine indexes - i.e. kept out of the listings of any relevant SERPs.
If your site is "banned", it is a very time-consuming process to get back into the index, and thus should be avoided at all costs - especially for an organisation with such a good reputation as the Victoria and Albert Museum.