Coinbase reported a terrible Q1 earnings card. It also corroborated our thesis that it's too challenging to accurately model COIN's revenue and profitability.Notably, the Street estimates missed its Q1 release significantly. As a result, investors need to ask themselves how to value COIN stock accurately if estimates are wildly speculative.Our previous speculative buy opportunity had reached our $200 price target before reversing. Therefore, we hope that readers who followed our rating on Coinbase stock have already exited their positions.We discuss why we revise our rating on COIN stock from speculative buy to Hold for now.