I'm 5'-11" and my bikes are 57 cm and 56 cm. I think a 54 cm may be a bit small. Try dealing with manager/owner or go to another shop. Buy the bike from the shop that seems the friendliest, most knowledgeable, helpful, etc.
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The Lord is merciful and gracious, slow to anger and abounding in steadfast love. - Psalm 103:8
I am a cyclist. I am not the fastest or the fittest. But I will get to where I'm going with a smile on my face.