related-by-current-product.liquid

<!-- Begin related product -->
<div class="recommended-products">
    <h2 class="section-title">YOU MAKE LIKE</h2>
    <ul class="
          product-row
          uniform-layout
          under-style
          rows-of-4">
        {% assign vendor = product.title %}
        {% assign vendor_handle = vendor | handleize %}
        {% assign handle = product.handle %}
        {% assign counter = '' %}
        {% paginate collections.all.products by 1000 %}
        {% for related_product in collections.all.products %}
            {% if vendor == related_product.title and counter.size < 4 and handle != related_product.handle %}
                {% capture temp %}{{ counter }}*{% endcapture %}
                {% assign counter = temp %}
                <li class="product-list-item">
                    {% if related_product.price_min < related_product.compare_at_price_min %}
                        {% if settings.show_sale_circle %}
                            <span class="circle sale">Sale</span>
                        {% endif %}
                    {% endif %}

                        <a href="{{ related_product.url }}">
                            <img src="{{ related_product.featured_image | product_img_url: 'large' }}" alt="{{ related_product.title | escape  }}" />
                        </a>

                    <div class="product-list-item-details">
                        <a href="{{ related_product.url }}" class="clearfix">
                            <h4 class="product-list-item-title">{{ related_product.title }}</h4>               
                            <h4 class="product-list-item-title font-weight">{{ related_product.tags.first | link_to_tag: product.tags.first }}</h4>
                
                            {% if settings.product_vendor %}
                                <span class="vendor">{{ related_product.vendor }}</span>
                            {% endif %}

                            <p class="product-list-item-price"><span class="price-money"></span>
                              {% if related_product.available %}
                                  {% if related_product.compare_at_price_max > related_product.price %}
                                      <p class="product-list-item-price">{{ related_product.compare_at_price | money }}</p>
                                  {% endif %}
                              {% if related_product.price_varies %}
                                  <small>from</small>
                              {% endif %}
                                  {{ related_product.price | money }}
                              {% else %}
                                  {{ related_product.price | money }} Sold Out
                              {% endif %}
                            </p>
                        </a>
                    </div>
                </li>
            {% endif %}
        {% endfor %}
        {%- endpaginate -%}
    </ul>
</div>

logic for custom related items example https://snapbook.com/collections/cases/products/moroccan-pattern