Thermometers

Older thermometers often contain mercury. Mercury is a dangerous substance, and disposing of or selling mercury thermometers is covered by hazardous waste rules.

See this guidance (pages 8-9):

Waste management: measuring devices containing mercury are classed as hazardous waste. To dispose of them, you'll need to have them removed by a registered waste carrier to a permitted waste disposal site. This does not endorse any particular disposal process or contractor.

Domestic mercury waste: mercury should not be disposed of in household waste. If you're a householder, your local authority can advise on how and where to dispose of your waste measuring devices, or you can search business directories for hazardous waste disposal contractors.

There are exemptions for devices over 50 years old, but unless there's some indication that the thermometer offered or requested isn't working, or will be used for something other than measuring, it should be fine to accept - perhaps with a mention of hazardous waste if there's any concern.

See also this Discourse discussion.

Link: Specific Items