Legal opinion

Need an opinion on the ability of buyers to on sell, freely, a particular type of product that does not have an explicit non-transferrable clause within its offer terms and conditions. Would need to understand the rights and remedies of primary sellers wishing to block, for whatever reason, such secondary sales, without their prior permission, and the relevant UK/European law, if known. In a similar vein where non transferable language exists in terms for related products, secondary sales are occurring without prior permission. Would like to know why? This project would suit a legal professional with exposure to and/or experience in the events industry.