There's no such thing as a safe place to auction off anything. The potential downside is just as great as the potential upside. If you want safety, sell fixed price, and wait longer for your money.
I have my own website, but used to use eBay a lot for finding new customers, and now have moved more coins to USACoinBook.com for that purpose.
EBay but....learn the ropes first. Learn and read what EBay coin sellers do. Be patient / wait and watch. Then, when you are ready decide a 'bid' deal or a Buy it Now deal. If this is not satisfactory try Heritage or Great Collections. Hope this helps.
What kind of stuff do you have? Some dealers do consignment which is better for you than outright sales, depending on how fast you want your money
If you sell yourself, take excellent pictures. Bad pictures are the single biggest reason why coins sell for a fraction of what they are worth in auctions.
eBay but learn how execute there. Get some experience there see what works for you. Over $50 stuff I start at blue sheet or slightly lower. Bullion I items start at 90-95 pct melt. Primarily there to retail from my online store stuff picked off online auction or from my table at shows. Goal: buy low / sell high. Get a feel on what will generate bidders what level suitable start for you. Once auction has 24 hours left you can’t end it but before that you can end it if not getting expected results relist or just throw back in store at retail. Have done this then item sells at retail week or so later. I strongly recommend the $28 a month eBay store (up to 250 items). Why not sell at retail vs give it away at auction? Have retailed stuff there thought chance nil. Realize at auction venues where buyers fees bidders will adjust their bid downward to avoid this. Then you get hit w sellers fee which means you would have been better shopping the coins around at a show offering at 80-85 pct bid. Learn how to handle cheapo tire kickers and people who won’t pay the money. Charge shipping or have a transaction fee tack on to handle shipping and fixed overhead in your free ship listings. I shop eBay pickoff stuff to retail at shows and my online store. Also buy books, games, supplies, clothes off the bay get eBay bucs. As far as those who bash ebay I believe many are simply incompetent, or very wealthy collectors (one I know of a silent partner in a coin dealership) plus big gun rich dealers / players who have their own agenda (angle or racket) and resent the competition from the bay (and the opportunity it affords the little guy) the worlds largest coin show. Example: Listed an NGC PF69DC mod $5 commem I had $320 in $5 below melt at $355 in bay auction. Was not moving / long time in inventory. One day into auction guy offered me $350 which I took. Had listed it 2x before $5 below melt, no bids. I used that money to buy a cac MS65 Boone silver commem and a Mexican silver Pcgs 19th century Pcgs 65 silver 20 centavos with top pop of only 2 graded none higher. Both coins bought at another auction venue and offer better chance for retail.
I like the auctions at www.davidlawrence.com. They charge a seller's premium of 10%, but there is no buyer's premium, and they offer free shipping. You can specify a starting bid if you want to make sure you receive a minimum amount for your coin(s).
There are Facebook Coin Groups for selling & buying coins & paper money. You need to request to be added to the group and be approved. Most all group members are very honest & relabel, those that are not are quickly banned from the groups. Some Facebook groups are managed by ANA professional persons. Most all require a PayPal account for payments. You can also use USPS MO or cash. There are no fees for posting an item for sale or buying, only if you use PayPal for payment. Good Luck
As stated above, know your stock. USAcoinbook is nice, I also recommend Vcoins (https://www.vauctions.com). I imagine Ebay gets most traffic, but be careful.