I'm so glad you listened to the voice inside that told you not to go through with this.
If any part of you is hesitating because you think it might be real, I promise you if someone went to buy a coffin they'd get a lot of questions about why they were buying one that wasn't being delivered to a funeral home. In some U.S. states, it is illegal to purchase a casket from somewhere other than a funeral home, in fact. And if you went to a funeral home and tried to buy a casket without a body to put in it, I'm not so sure that would fly. That right there tells you this person was not being truthful with you, and you can safely just block and ignore this person. All that would have happened is you'd be out a lot of money.
I'm glad you didn't go that route!
Also, as for feeling guilty about not saying goodbye - girl, this person tried to defraud you. This person attempted to LITERALLY STEAL YOUR MONEY. You don't owe this person shit. In fact, I'd like to put my boot where the sun don't shine on your behalf. Do not waste another minute thinking about this fraud, and she sure as hell does not deserve your courtesy.