Can my landlord accept money from me after a eviction was in place and then come to verbal agreement about payment of the remainder amount due but turn around and serve a writ of ejectment before thirty days is even up?

If its not in writing... it will be extremely difficult to prove it ever took place. Especially if the transaction took place in cash. Its your word against someone else's.

And in any event... the eviction doesn't end your liability for past due debts... you would have still owed them... and been sued for them in court after the eviction if the landlord so decided.