Only one live one has been seen but it was dying. They do give scientists a lot of information about this mysterious cephalopod but they don't give them all the information. The size of the giant squid are sometimes estimated by these dead specimens. However, scientists sometimes stretch the arms more than they probably would be in the real world so estimations have been exaggerated. Size estimates have also been based on scars on sperm whales.
Suckers leave scars on sperm whales when the squid are being attacked.
Large sucker marks are used to estimate giant squid sizes but some of those scars may have grown as the sperm whales have grown. Some large scars have also been newly attributed to the bite marks of cookie cutter sharks, which leave a large round scar similar to the giant squids sucker scars but bigger. It is extremely difficult to study these creatures for no giant squid has ever been witnessed in the wild. Where they live and feed is unknown, however small fish and other squid have been found within the stomachs of specimens. Scientists estimate that the squid live within the deep, dark waters of 1000ft-2000ft and may be near sperm whale populations.