For example, let's say I have an SaaS application, that enables users help create Telegram bot. On the server, we process the bots and APIs for it. Now, let's say if some users try to use the application for bad purpose, like spamming, scamming, illegal activity. Now, are we responsible for the user's usage? What type of workarounds or disclaimer can we have to avoid these troubles?
Yes - if your accounts are being used, you will be billed, and you would be liable to the SaaS provider for costs racked up. Its less likely, but the SaaS provider could terminate your service for a breach of their T&C's.
Ways to mitigate the risk could include setting up the service in your clients name ( ie they pay for the SaaS service + some kind if license fee for you to maintain the system for them ).
Alternatively a combinatiion of a bond and close monitoring of your server and/or limits per user - alongside appropriate protectiions and termination/suspension clauses in your agreements are a practical middle ground.