It's an unfortunate fact that a major crisis like this brings out the low life and bottomfeeders. From profiteering to outright scams and criminality.
There have been reports of people pretending to be NHS staff raising money, either on the phone or banging on doors, to people offering fake Coronavirus vaccines. Along with the usual doorstep scams, such as tradesmen offering to fix nonexistent urgent issues.
The best defence is always to say "No Thanks". Don't feel guilty, if you want to donate to a good cause, then you decide when and where.
If someone is genuine, they can leave information, won't pressure you, allowing you to research, ask advice and contact them back at a later date if appropriate.
With more older or vulnerable people self-isolating, the risk is higher, so make sure elderly relatives or neighbours understand to say no thanks to phone calls, doorstep traders, pleas for cash or offers of miracle vaccines.