Tenant has no income but money upfront - too risky?

[Mary Ainsworth]

I know people say not to accept tenants if they have no active income, but this is a medium-term tenant who would stay 3 months and they can pay the entire 3 months upfront. In this case, is it a risk to let them stay? 

My only thought is that they could try to stay there and refuse to leave I suppose, but that's a risk even when someone has active income coming in. 

Also, if they have a guarantor, would that help? I'm not sure it would since they're paying all three months upfront, but I had that thought

Any advice would be great! Thank you :)