In most cases, guarantors will fill out the same application as a full lessee. The difference being that some landlords require only a credit screening and not the full criminal + eviction history check for the guarantor.
As with a co-signer, the risks lie primarily with the guarantor. If you're a guarantor, you might have to shoulder a financial burden on behalf of the borrower, which can be a challenge even for someone with high credit scores. Still, you'll have the satisfaction of enabling a loved one's access to important credit.
It will still be hard because guarantors are usually for students, and most landlords will expect working tenants to make 2.5 to 3 times the rent as you say, but you'll have a better chance than if you don't go into the details of your situation.
If a prospective renter doesn't meet those criteria, they should consider finding a guarantor who has a credit score of 700 or higher and an annual income of at least 80 times the monthly rent. For example, if the rent is $2,000 a month, the guarantor would need to make at least $160,000 a year.