Online sellers are always interested in learning what products to sell for the summer. This isn't really as complicated as it seems. Pay attention to what is going on around you and watch what the major retailers are doing, then follow suit.
One of the first things that comes to mind when you think of spring and summer is bugs! Insect control products are great sellers on eBay during the spring and summer months. Products like bug zappers, citronella candles, and insect repellent towelettes will be popular. Smaller items like citronella bracelets and candles can be sold in large lots for outdoor events like family reunions, vacation bible school, and summer day camps. I recently sold a case of 24 citronella bracelets on eBay.
Another popular niche is outdoor cooking, barbecues, and grilling. Research products like grill utensil sets, grill covers, personalized aprons for men (Father's Day), thermometers, and lighters. Think about your own "grill master" and what that person uses.
Summer also means water sports. Items like life jackets (even for pets), boating accessories, swimwear, baby floats, goggles, and sunscreen. Think about consumable products (like sunscreen and insect repellent towelettes) that get used up and must be replenished. Consumables are one of the most profitable and sustainable niches on eBay.
More ideas on products to look for at thrift stores during the warm months: