The law states that the tenant must return the property in similar condition to how it was offered which means that every little scratch the landlord finds will have to be repaired. But the law also requires the landlord to provide an itemized list of repairs necessary to the tenant within a certain time period by state law (and they do differ) proving why the deposit is being kept partially or in full. Typically this period is between 2-6 weeks. If the landlord fails to provide this written notice to the tenant the tenant can sue the landlord for their deposit and get back with ease. But when this does happen the landlord usually counter-sues for their damage claim. But you are also right that the length of time that passes with the tenant not in the property, it makes it harder for the landlord to prove the damage occurred in your possession.

If your friends caused damage that is beyond wear and tear, then they are responsible for the cost to repair/replace the damaged items.

If the place already had damages, they needed to photograph the damages and report them to the landlord. Additionally, if lights stopped working during their tenancy, it was their obligation to report the issues immediately. When they moved out, they should have done a walkthrough, with a checklist and with a camera, and had the landlord sign off on it.

In most states, the landlord cannot just "keep bugging them". He must send an itemized statement of the damages and the cost to repair them within a certain period of time. If this was done and your friends are refusing to pay, yes, the landlord can take them to civil court.

He should use the walk thru papers and pictures he took with the landlord when he left and compare them to the ones he took when he moved in. Oh yeah he probably didn't do that. He has no way to prove he didn't do it. Your state has laws on how long until the landlord must submit you a letter in writing with damages and a refund of your deposit. He cannot keep bugging him.

this is the reason that you as a tenant want to take pictures when you move in and again when you move out

the landlord can claim a lot of things that may or may not have occurred during your rental but you have no way to disprove without pictures or a signed 'walk thru' at the time when you rented

Ok I'm not experienced at all with this but a friend is worried and told me that they rented a house from someone for a while and now they left and the owner is back, so for 2 straight months the owner kept bugging them about small thing they have to pay for like a dent in the wall or a scratch on the front door or that the lights is messed up. And he keeps going for two months. Some of this stuff might have happened while the owner was there, and he's saying it was my friends fault. He threatened to sue. Can he do that? Also is their some kind of law that limits the time to charge the damages made from the previous owner? Sorry if it doesn't make sense, any advice will help thanks.